# Maths

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huge mess. also working back from Computing#Computation

## Contents

- 1 General
- 2 Systems
- 2.1 Formalism
- 2.2 Constructivism
- 2.3 to sort
- 2.4 Algebra
- 2.5 Model theory
- 2.6 Proof theory
- 2.7 Structures
- 2.8 Arithmetic
- 2.9 Morphisms
- 2.10 Logic
- 2.10.1 Boolean algebra / propositional calculus/logic
- 2.10.2 Predicate / first-order logic
- 2.10.3 Other logics
- 2.10.4 Categorical logic
- 2.10.5 Proof calculus
- 2.10.6 Sequent calculus
- 2.10.7 Linear logic
- 2.10.8 Sequential logic
- 2.10.9 Combinatorial logic
- 2.10.10 to sort
- 2.10.11 Non-classical logic
- 2.10.12 Fuzzy logic
- 2.10.13 Modal logic
- 2.10.14 to sort
- 2.10.15 to sort

- 2.11 Domain theory
- 2.12 Analysis
- 2.13 Calculus
- 2.14 Type theory
- 2.15 Combinatorics

- 3 Geometry
- 4 Probability theory
- 5 Information theory
- 6 Cellular automaton
- 7 Software
- 8 Visualisation
- 9 Informatics
- 10 Nature
- 11 to sort

## General

to sort

- YouTube: The Map of Mathematics

- https://en.wikipedia.org/wiki/Areas_of_mathematics
- https://en.wikipedia.org/wiki/Mathematics_Subject_Classification

- http://mathwithbaddrawings.com/
- http://www.mathsisfun.com/index.htm
- http://betterexplained.com/articles/category/math/

- https://en.wikipedia.org/wiki/Theorem - a statement that has been proven on the basis of previously established statements, such as other theorems—and generally accepted statements, such as axioms. The proof of a mathematical theorem is a logical argument for the theorem statement given in accord with the rules of a deductive system. The proof of a theorem is often interpreted as justification of the truth of the theorem statement. In light of the requirement that theorems be proved, the concept of a theorem is fundamentally deductive, in contrast to the notion of a scientific theory, which is empirical.

- https://en.wikipedia.org/wiki/Lemma_(mathematics) - (plural lemmata or lemmas) from the Greek λῆμμα (lemma, “anything which is received, such as a gift, profit, or a bribe”) or helping theorem is a proven proposition which is used as a stepping stone to a larger result rather than as a statement of interest by itself. There is no formal distinction between a lemma and a theorem, only one of intention – see Theorem terminology. However, a lemma can be considered a minor result whose sole purpose is to help prove a theorem - a step in the direction of proof, so to speak.
- https://en.wikipedia.org/wiki/List_of_lemmas

- https://en.wikipedia.org/wiki/Fundamental_theorem - the theorem considered central to a field of mathematics. The naming of such a theorem is not necessarily based on how often it is used or the difficulty of its proofs. For example, the fundamental theorem of calculus gives the relationship between differential calculus and integral calculus, which are two distinct branches that were not obviously related. The names are mostly traditional, so that for example the fundamental theorem of arithmetic is basic to what would now be called number theory.

- https://en.wikipedia.org/wiki/Superposition_principle
- https://en.wikipedia.org/wiki/Nonlinear_system

- http://en.wikipedia.org/wiki/Mathematical_objects mathematical object] - an abstract object arising in philosophy of mathematics and mathematics. Commonly encountered mathematical objects include numbers, permutations, partitions, matrices, sets, functions, and relations. Geometry as a branch of mathematics has such objects as hexagons, points, lines, triangles, circles, spheres, polyhedra, topological spaces and manifolds. Algebra, another branch, has groups, rings, fields, group-theoretic lattices, and order-theoretic lattices. Categories are simultaneously homes to mathematical objects and mathematical objects in their own right.

### Learning

- Better Explained - Math lessons that actually explain concepts. [5]
- Better Maths Intuition Cheatsheet - Math is no more about equations than poetry is about spelling. Find your Aha! Moment.

- PDF: A Mathematician’s Lament by Paul Lockhart
- 5-Year-Olds Can Learn Calculus [6]

- Most Math Problems Do Not Have a Unique Right Answer [8]
- Mathematicians are chronically lost and confused (and that’s how it’s supposed to be) [9]

- European Digital Mathematics Library (EuDML) - mathematics literature available online in the form of an enduring digital collection, developed and maintained by a network of institutions.

- MatematicasVisuales - visual expositions of mathematical concepts. phttps://news.ycombinator.com/item?id=8732801]

- YouTube: Introduction to Higher Mathematics by Bill Shillito

### Tools

- Mathway provides students with the tools they need to understand and solve their math problems. With hundreds of millions of problems already solved, Mathway is the #1 problem solving resource available for students, parents, and teachers.

- Webmath is a math-help web site that generates answers to specific math questions and problems, as entered by a user, at any particular moment.

- Desmos Graphing Calculator – HTML5 with LaTeX editor [13]

### History

- https://thonyc.wordpress.com/2017/02/10/the-widespread-and-persistent-myth-that-it-is-easier-to-multiply-and-divide-with-hindu-arabic-numerals-than-with-roman-ones/ [15]

- A Prayer for Archimedes - A long-lost text by the ancient Greek mathematician shows that he had begun to discover the principles of calculus.

- YouTube: More Hiking in Modern Math World
- YouTube: A Trek through 20th Century Mathematics

### Social

- Function Space is a social learning network for science with complete ecosystem (articles, video lectures, problem solving, discussions, and networking) for participants from academia to corporate research. We intend to bridge the gap between academic curriculum and skill based requirements of workplace.

- Polymath1Wiki - massively collaborative online mathematical projects

### Books

### Other

### Research

- zbMATH (Zentralblatt MATH) is the world’s most comprehensive and longest-running abstracting and reviewing service in pure and applied mathematics. It is produced by the Berlin office of FIZ Karlsruhe – Leibniz Institute for Information Infrastructure GmbH (FIZ Karlsruhe). Editors are the European Mathematical Society (EMS), FIZ Karlsruhe, and the Heidelberg Academy of Sciences and Humanities. zbMATH is distributed by Springer. The zbMATH database contains more than 3.5 million bibliographic entries with reviews or abstracts currently drawn from more than 3,000 journals and serials, and 170,000 books. The coverage starts in the 18th century and is complete from 1868 to the present by the integration of the “Jahrbuch über die Fortschritte der Mathematik” database. About 7,000 active expert reviewers from all over the world contribute reviews to zbMATH.

zbMATH provides easy access to bibliographic data, reviews and abstracts from all areas of pure mathematics as well as applications, in particular to the natural sciences, computer science, economics and engineering. It also covers history and philosophy of mathematics and university education. All entries are classified according to the Mathematics Subject Classification Scheme (MSC 2010) and are equipped with keywords in order to characterize their particular content. zbMATH covers all available published and peer-reviewed articles, books, conference proceedings as well as other publication formats pertaining to the scope given above. For the list of journals and book series covered see the Journals search.

### People

## Systems

meeeess

### Formalism

- https://en.wikipedia.org/wiki/Formal_language - well-defined vocabulary and grammar

- YouTube: Odd Equations - Numberphile

- Category Theory for the Working Hacker - Philip Wadler on why category theory is relevant for developers, discussing the principle of Propositions as Types connecting propositions and proofs in logic, and types and programs in computing. [20]

### Constructivism

#### Intuitionism

#### Univalent foundations

- (−2)-types are the contractible ones,
- (−1)-types are the truth values,
- 0-types are the sets,
- 1-types are the groupoids,
- etc.

### to sort

- https://en.wikipedia.org/wiki/Natural_deduction - a kind of proof calculus in which logical reasoning is expressed by inference rules closely related to the "natural" way of reasoning. This contrasts with the axiomatic systems which instead use axioms as much as possible to express the logical laws of deductive reasoning.

- https://en.wikipedia.org/wiki/Domain_of_discourse - also called the universe of discourse (or simply universe), is the set of entities over which certain variables of interest in some formal treatment may range.

- https://en.wikipedia.org/wiki/Theorem - a statement that has been proven on the basis of previously established statements, such as other theorems—and generally accepted statements, such as axioms. The proof of a mathematical theorem is a logical argument for the theorem statement given in accord with the rules of a deductive system. The proof of a theorem is often interpreted as justification of the truth of the theorem statement. In light of the requirement that theorems be proved, the concept of a theorem is fundamentally deductive, in contrast to the notion of a scientific theory, which is empirical.

- https://en.wikipedia.org/wiki/Quantification#Logic
- https://en.wikipedia.org/wiki/Universal_quantification - all or any - universal - ∀
- https://en.wikipedia.org/wiki/Existential_quantification - there exists - particular - ∃

- https://en.wikipedia.org/wiki/Formal_proof - or derivation, is a finite sequence of sentences, each of which is an axiom or follows from the preceding sentences in the sequence by a rule of inference

- https://en.wikipedia.org/wiki/Well-formed_formula - proof in a formal system

An ordinary formal system differs from a logical calculus in that the system usually has an intended interpretation, whereas the logical calculus deliberately leaves the possible interpretations open. Thus, one speaks, for example, of the truth or falsity of sentences in a formal system, but with respect to a logical calculus one speaks of validity (i.e., being true in all interpretations or in all possible worlds) and of satisfiability (or having a model—i.e., being true in some particular interpretation). Hence, the completeness of a logical calculus has quite a different meaning from that of a formal system: a logical calculus permits many sentences such that neither the sentence nor its negation is a theorem because it is true in some interpretations and false in others, and it requires only that every valid sentence be a theorem.

- https://en.wikipedia.org/wiki/Consistency - In classical deductive logic, a consistent theory is one that does not contain a contradiction. The lack of contradiction can be defined in either semantic or syntactic terms. The semantic definition states that a theory is consistent if and only if it has a model, i.e. there exists an interpretation under which all formulas in the theory are true. This is the sense used in traditional Aristotelian logic, although in contemporary mathematical logic the term satisfiable is used instead. The syntactic definition states that a theory is consistent if and only if there is no formula P such that both P and its negation are provable from the axioms of the theory under its associated deductive system.

If these semantic and syntactic definitions are equivalent for any theory formulated using a particular deductive logic, the logic is called complete. The completeness of the sentential calculus was proved by Paul Bernays in 1918[citation needed] and Emil Post in 1921, while the completeness of predicate calculus was proved by Kurt Gödel in 1930, and consistency proofs for arithmetics restricted with respect to the induction axiom schema were proved by Ackermann (1924), von Neumann (1927) and Herbrand (1931). Stronger logics, such as second-order logic, are not complete.

- https://en.wikipedia.org/wiki/Metatheorem - a statement about a formal system proven in a metalanguage. Unlike theorems proved within a given formal system, a metatheorem is proved within a metatheory, and may reference concepts that are present in the metatheory but not the object theory.

A formal system is determined by a formal language and a deductive system (axioms and rules of inference). The formal system can be used to prove particular sentences of the formal language with that system. Metatheorems, however, are proved externally to the system in question, in its metatheory. Common metatheories used in logic are set theory (especially in model theory) and primitive recursive arithmetic (especially in proof theory). Rather than demonstrating particular sentences to be provable, metatheorems may show that each of a broad class of sentences can be proved, or show that certain sentences cannot be proved

- https://en.wikipedia.org/wiki/Mathematical_induction - an inference rule, not inductive reasoning

- http://math.andrej.com/2010/03/29/proof-of-negation-and-proof-by-contradiction/
- https://gowers.wordpress.com/2010/03/28/when-is-proof-by-contradiction-necessary/ [21]

- https://en.wikipedia.org/wiki/Category:Systems_of_formal_logic
- https://en.wikipedia.org/wiki/List_of_logic_systems

### Algebra

- https://en.wikipedia.org/wiki/Algebra - one of the broad parts of mathematics, together with number theory, geometry and analysis. In its most general form, algebra is the study of mathematical symbols and the rules for manipulating these symbols; it is a unifying thread of almost all of mathematics. As such, it includes everything from elementary equation solving to the study of abstractions such as groups, rings, and fields. The more basic parts of algebra are called elementary algebra; the more abstract parts are called abstract algebra or modern algebra. Elementary algebra is generally considered to be essential for any study of mathematics, science, or engineering, as well as such applications as medicine and economics. Abstract algebra is a major area in advanced mathematics, studied primarily by professional mathematicians.

Elementary algebra differs from arithmetic in the use of abstractions, such as using letters to stand for numbers that are either unknown or allowed to take on many values. For example, in *x+2=5* the letter *x* is unknown, but the law of inverses can be used to discover its value: *x=3*. In *E = mc2*, the letters *E* and *m* are variables, and the letter *c* is a constant, the speed of light in a vacuum. Algebra gives methods for solving equations and expressing formulas that are much easier (for those who know how to use them) than the older method of writing everything out in words.

The word algebra is also used in certain specialized ways. A special kind of mathematical object in abstract algebra is called an "algebra", and the word is used, for example, in the phrases linear algebra and algebraic topology.

https://en.wikipedia.org/wiki/Algebraic_operation

- http://www.cut-the-knot.org/ctk/between.shtml
- http://profkeithdevlin.org/2011/11/20/what-is-algebra/

- https://en.wikipedia.org/wiki/Expression_(mathematics) - a finite combination of symbols that is well-formed according to rules that depend on the context. Symbols can designate numbers (constants), variables, operations, functions, and other mathematical symbols, as well as punctuation, symbols of grouping, and other syntactic symbols.

- https://en.wikipedia.org/wiki/Equation - a formula of the form A = B, where A and B are expressions that may contain one or several variables called unknowns, and "=" denotes the equality binary relation. Although written in the form of proposition, an equation is not a statement that is either true or false, but a problem consisting of finding the values, called solutions, that, when substituted for the unknowns, yield equal values of the expressions A and B.

- https://en.wikipedia.org/wiki/Equality_(mathematics) - relationship between two quantities or, more generally two mathematical expressions, asserting that the quantities have the same value or that the expressions represent the same mathematical object

- https://en.wikipedia.org/wiki/Nth_root - the nth root of a number x is a number r which, when raised to the power of n, equals x
- https://en.wikipedia.org/wiki/Square_root
- https://en.wikipedia.org/wiki/Cube_root

- https://en.wikipedia.org/wiki/Root-finding_algorithm
- https://en.wikipedia.org/wiki/Methods_of_computing_square_roots

- https://en.wikipedia.org/wiki/Fundamental_theorem_of_algebra
- YouTube: Fundamental Theorem of Algebra - Numberphile

- https://en.wikipedia.org/wiki/Polynomial - an expression consisting of variables (or indeterminates) and coefficients, that involves only the operations of addition, subtraction, multiplication, and non-negative integer exponents.

- https://en.wikipedia.org/wiki/Algebraic_equation - or polynomial equation is an equation of the form P = Q where P and Q are polynomials with coefficients in some field, often the field of the rational numbers. For most authors, an algebraic equation is univariate, which means that it involves only one variable. On the other hand, a polynomial equation may involve several variables, in which case it is called multivariate and the term polynomial equation is usually preferred to algebraic equation.

#### Abstract algebra

- YouTube: Basic abstract algebra, pt.1 - slides w/ music

- https://www.youtube.com/watch?v=IP7nW_hKB7I&list=PLi01XoE8jYoi3SgnnGorR_XOW3IcK-TP6 https://www.youtube.com/watch?v=QudbrUcVPxk&list=PLi01XoE8jYoi3SgnnGorR_XOW3IcK-TP6

- https://en.wikipedia.org/wiki/Algebraic_structure - a set (called carrier set or underlying set) with one or more finitary operations defined on it that satisfies a list of axioms.

Examples of algebraic structures include groups, rings, fields, and lattices. More complex structures can be defined by introducing multiple operations, different underlying sets, or by altering the defining axioms. Examples of more complex algebraic structures include vector spaces, modules, and algebras.

The properties of specific algebraic structures are studied in abstract algebra. The general theory of algebraic structures has been formalized in universal algebra. The language of category theory is used to express and study relationships between different classes of algebraic and non-algebraic objects. This because it is sometimes possible to find strong connections between some classes of objects, sometimes of different kinds. For example, Galois theory establishes a connection between certain fields and groups: two algebraic structures of different kinds.

#### Universal algebra

- https://en.wikipedia.org/wiki/Universal_algebra - sometimes called general algebra) is the field of mathematics that studies algebraic structures themselves, not examples ("models") of algebraic structures. For instance, rather than take particular groups as the object of study, in universal algebra one takes "the theory of groups" as an object of study.

#### Category theory

- https://en.wikipedia.org/wiki/Category_theory - deals in an abstract way with mathematical structures and relationships between them. abstract algebra for more than just algebra..

Category theory is a mathematical approach to the study of algebraic structure that has become an important tool in theoretical computing science, particularly for semantics-based research. The aim of this course is to teach the basics of category theory, in a way that is accessible and relevant to computer scientists. The emphasis is on gaining a good understanding the basic definitions, examples, and techniques, so that students are equipped for further study on their own of more advanced topics if required.

- YouTube: Category Theory - Category theory for programmers by Bartosz Milewski. Seattle, Summer 2016.

- Introduction to Category Theory - Graham Hutton, School of Computer Science, University of Nottingham.

- YouTube: Category theory foundations 1.0 — Steve Awodey
- YouTube: Category Theory by Tom LaGatta

- An Elementary Theory of the Category of Sets - alternative to ZFC
- http://golem.ph.utexas.edu/category/2014/01/an_elementary_theory_of_the_ca.html
- http://ncatlab.org/nlab/show/ETCS
- http://ncatlab.org/nlab/show/Trimble+on+ETCS+I

- nLab is a wiki-lab for collaborative work on Mathematics, Physics and Philosophy — especially from the n-point of view: insofar as these subjects are usefully treated with tools and notions of category theory or higher category theory.

- Category theory definition dependencies - diagram showing how category theory definitions build on each other.

### Model theory

- http://en.wikipedia.org/wiki/Model_theory - the study of classes of mathematical structures (e.g. groups, fields, graphs, universes of set theory) from the perspective of mathematical logic. The objects of study are models of theories in a formal language. We call a theory a set of sentences in a formal language, and model of a theory a structure (e.g. an interpretation) that satisfies the sentences of that theory.

Model theory recognises and is intimately concerned with a duality: It examines semantical elements (meaning and truth) by means of syntactical elements (formulas and proofs) of a corresponding language. To quote the first page of Chang and Keisler (1990):

- universal algebra + logic = model theory.

Model theory developed rapidly during the 1990s, and a more modern definition is provided by Wilfrid Hodges (1997):

- model theory = algebraic geometry − fields

although model theorists are also interested in the study of fields. Other nearby areas of mathematics include combinatorics, number theory, arithmetic dynamics, analytic functions, and non-standard analysis.

In a similar way to proof theory, model theory is situated in an area of interdisciplinarity among mathematics, philosophy, and computer science. The most prominent professional organization in the field of model theory is the Association for Symbolic Logic.

### Proof theory

- http://en.wikipedia.org/wiki/Proof_theory - a major branch of mathematical logic that represents proofs as formal mathematical objects, facilitating their analysis by mathematical techniques. Proofs are typically presented as inductively-defined data structures such as plain lists, boxed lists, or trees, which are constructed according to the axioms and rules of inference of the logical system. As such, proof theory is syntactic in nature, in contrast to model theory, which is semantic in nature.

Some of the major areas of proof theory include structural proof theory, ordinal analysis, provability logic, reverse mathematics, proof mining, automated theorem proving, and proof complexity. Much research also focuses on applications in computer science, linguistics, and philosophy.

### Structures

#### Sets

- https://ncatlab.org/nlab/show/Set - Set is the (or a) category with sets as objects and functions between sets as morphisms.

- https://en.wikipedia.org/wiki/Element_(mathematics) - or
**member**, of a set is any one of the distinct objects that make up that set.

- https://en.wikipedia.org/wiki/Cardinality - a measure of the "number of elements of the set"

- https://en.wikipedia.org/wiki/Singleton_(mathematics) - also known as a unit set, is a set with exactly one element. For example, the set {0} is a singleton. The term is also used for a 1-tuple (a sequence with one member).

- https://en.wikipedia.org/wiki/Class_(set_theory) - collection of sets (or other mathematical objects) with a property that all its members share

- https://en.wikipedia.org/wiki/Continuum_(set_theory) - means the real numbers, or the corresponding (infinite) cardinal number, c. Georg Cantor proved that the cardinality c is larger than the smallest infinity, namely, aleph 0. He also proved that c equals 2^aleph 0, the cardinality of the power set of the natural numbers.

- https://en.wikipedia.org/wiki/Cardinality_of_the_continuum - the size of the set of real numbers

- https://en.wikipedia.org/wiki/Continuum_hypothesis - sometimes stated by saying that no cardinality lies between that of the continuum and that of the natural numbers, aleph 0.

- https://en.wikipedia.org/wiki/Aleph_number - aleph numbers are a sequence of numbers used to represent the cardinality (or size) of infinite sets

- https://en.wikipedia.org/wiki/Countable_set - set with the same cardinality as some subset of the set of natural numbers
- https://en.wikipedia.org/wiki/Uncountable_set - cardinal number is larger than that of the set of all natural numbers

- https://en.wikipedia.org/wiki/Axiomatic_set_theory
- https://en.wikipedia.org/wiki/Zermelo%E2%80%93Fraenkel_set_theory

- https://en.wikipedia.org/wiki/Von_Neumann%E2%80%93Bernays%E2%80%93G%C3%B6del_set_theory
- https://math.stackexchange.com/questions/136215/difference-between-zfc-nbg

- https://en.wikipedia.org/wiki/Power_set - the set of all subsets of S, including the empty set and S itself. The power set of a set S is variously denoted as P(S), ℘(S) (using the "Weierstrass p"), P(S), ℙ(S), or, identifying the powerset of S with the set of all functions from S to a given set of two elements, 2S. In axiomatic set theory (as developed, for example, in the ZFC axioms), the existence of the power set of any set is postulated by the axiom of power set. Any subset of P(S) is called a family of sets over S.

- https://en.wikipedia.org/wiki/Hasse_diagram - a type of mathematical diagram used to represent a finite partially ordered set, in the form of a drawing of its transitive reduction.

#### Groups

- https://en.wikipedia.org/wiki/Group_(mathematics) - a set of elements together with an operation that combines any two of its elements to form a third element satisfying four conditions called the group axioms, namely closure, associativity, identity and invertibility. One of the most familiar examples of a group is the set of integers together with the addition operation; the addition of any two integers forms another integer.

The abstract formalization of the group axioms, detached as it is from the concrete nature of any particular group and its operation, allows entities with highly diverse mathematical origins in abstract algebra and beyond to be handled in a flexible way, while retaining their essential structural aspects. The ubiquity of groups in numerous areas within and outside mathematics makes them a central organizing principle of contemporary mathematics.

Groups share a fundamental kinship with the notion of symmetry. For example, a symmetry group encodes symmetry features of a geometrical object: the group consists of the set of transformations that leave the object unchanged and the operation of combining two such transformations by performing one after the other. Lie groups are the symmetry groups used in the Standard Model of particle physics; Point groups are used to help understand symmetry phenomena in molecular chemistry; and Poincaré groups can express the physical symmetry underlying special relativity.

The concept of a group arose from the study of polynomial equations, starting with Évariste Galois in the 1830s. After contributions from other fields such as number theory and geometry, the group notion was generalized and firmly established around 1870. Modern group theory—an active mathematical discipline—studies groups in their own right. To explore groups, mathematicians have devised various notions to break groups into smaller, better-understandable pieces, such as subgroups, quotient groups and simple groups.

In addition to their abstract properties, group theorists also study the different ways in which a group can be expressed concretely (its group representations), both from a theoretical and a computational point of view. A theory has been developed for finite groups, which culminated with the classification of finite simple groups announced in 1983. Since the mid-1980s, geometric group theory, which studies finitely generated groups as geometric objects, has become a particularly active area in group theory.

- YouTube: MathHistory20: Group theory

- YouTube: Visualizing Group Theory 1

- https://en.wikipedia.org/wiki/Group_action - a way of interpreting the elements of the group as "acting" on some space in a way that preserves the structure of that space. Common examples of spaces that groups act on are sets, vector spaces, and topological spaces. Actions of groups on vector spaces are called representations of the group.

- https://en.wikipedia.org/wiki/Additive_group - a group of which the group operation is to be thought of as addition in some sense. It is usually abelian, and typically written using the symbol + for its binary operation.

- https://en.wikipedia.org/wiki/Abelian_group - also called a
**commutative group**, is a group in which the result of applying the group operation to two group elements does not depend on their order (the axiom of commutativity). Abelian groups generalize the arithmetic of addition of integers.

- https://en.wikipedia.org/wiki/Non-abelian_group - also sometimes called a noncommutative group, is a group (G, * ) in which there are at least two elements a and b of G such that a * b ≠ b * a. The term nonabelian is used to distinguish from the idea of an abelian group, where all of the elements of the group commute.

Nonabelian groups are pervasive in mathematics and physics. One of the simplest examples of a nonabelian group is the dihedral group of order 6. It is the smallest finite nonabelian group. A common example from physics is the rotation group SO(3) in three dimensions (rotating something 90 degrees away from you and then 90 degrees to the left is not the same as doing them the other way round). Both discrete groups and continuous groups may be nonabelian. Most of the interesting Lie groups are nonabelian, and these play an important role in gauge theory.

- https://en.wikipedia.org/wiki/Subgroup - In mathematics, given a group G under a binary operation ∗, a subset H of G is called a subgroup of G if H also forms a group under the operation ∗. More precisely, H is a subgroup of G if the restriction of ∗ to H × H is a group operation on H. This is usually represented notationally by H ≤ G, read as "H is a subgroup of G".

A proper subgroup of a group G is a subgroup H which is a proper subset of G (i.e. H ≠ G). The trivial subgroup of any group is the subgroup {e} consisting of just the identity element. If H is a subgroup of G, then G is sometimes called an overgroup of H.

The same definitions apply more generally when G is an arbitrary semigroup, but this article will only deal with subgroups of groups. The group G is sometimes denoted by the ordered pair (G, ∗), usually to emphasize the operation ∗ when G carries multiple algebraic or other structures.

- https://en.wikipedia.org/wiki/Group_representation - describe abstract groups in terms of linear transformations of vector spaces; in particular, they can be used to represent group elements as matrices so that the group operation can be represented by matrix multiplication. Representations of groups are important because they allow many group-theoretic problems to be reduced to problems in linear algebra, which is well understood. They are also important in physics because, for example, they describe how the symmetry group of a physical system affects the solutions of equations describing that system.

The term representation of a group is also used in a more general sense to mean any "description" of a group as a group of transformations of some mathematical object. More formally, a "representation" means a homomorphism from the group to the automorphism group of an object. If the object is a vector space we have a linear representation. Some people use realization for the general notion and reserve the term representation for the special case of linear representations. The bulk of this article describes linear representation theory; see the last section for generalizations.

##### Simple groups

- http://en.wikipedia.org/wiki/Daniel_Gorenstein
- http://plus.maths.org/content/enormous-theorem-classification-finite-simple-groups

###### Group of Lie type

- https://en.wikipedia.org/wiki/Group_of_Lie_type - a group closely related to the group G(k) of rational points of a reductive linear algebraic group G with values in the field k. Finite groups of Lie type give the bulk of nonabelian finite simple groups. Special cases include the classical groups, the Chevalley groups, the Steinberg groups, and the Suzuki–Ree groups.

- https://en.wikipedia.org/wiki/Classical_group - defined as the special linear groups over the reals R, the complex numbers C and the quaternions H together with special automorphism groups of symmetric or skew-symmetric bilinear forms and Hermitian or skew-Hermitian sesquilinear forms defined on real, complex and quaternionic finite-dimensional vector spaces.

Of these, the complex classical Lie groups are four infinite families of Lie groups that together with the exceptional groups exhaust the classification of simple Lie groups. The compact classical groups are compact real forms of the complex classical groups. The finite analogues of the classical groups are the classical groups of Lie type. The term "classical group" was coined by Hermann Weyl, it being the title of his 1939 monograph The Classical Groups.

The classical groups form the deepest and most useful part of the subject of linear Lie groups. Most types of classical groups find application in classical and modern physics. A few examples are the following. The rotation group SO(3) is a symmetry of Euclidean spaaaaaace and all fundamental laws of physics, the Lorentz group O(3,1) is a symmetry group of spacetime of special relativity. The special unitary group SU(3) is the symmetry group of quantum chromodynamics and the symplectic group Sp(m) finds application in hamiltonian mechanics and quantum mechanical versions of it.

##### Sporadic group

#### Rings

- https://en.wikipedia.org/wiki/Ring_(mathematics) - one of the fundamental algebraic structures used in abstract algebra. It consists of a set equipped with two binary operations that generalize the arithmetic operations of addition and multiplication. Through this generalization, theorems from arithmetic are extended to non-numerical objects such as polynomials, series, matrices and functions.

- https://en.wikipedia.org/wiki/Commutative_ring - a ring in which the multiplication operation is commutative. The study of commutative rings is called commutative algebra.

Some specific kinds of commutative rings are given with the following chain of class inclusions:
**Commutative rings** ⊃ integral domains ⊃ integrally closed domains ⊃ unique factorization domains ⊃ principal ideal domains ⊃ Euclidean domains ⊃ fields

- https://en.wikipedia.org/wiki/Ideal_(ring_theory) - a special subset of a ring. Ideals generalize certain subsets of the integers, such as the even numbers or the multiples of 3. Addition and subtraction of even numbers preserves evenness, and multiplying an even number by any other integer results in another even number; these closure and absorption properties are the defining properties of an ideal. An ideal can be used to construct a quotient ring similarly to the way that, in group theory, a normal subgroup can be used to construct a quotient group.

- https://en.wikipedia.org/wiki/Principal_ideal - an ideal I in a ring R that is generated by a single element a of R through multiplication by every element of R. The term also has another, similar meaning in order theory, where it refers to an (order) ideal in a poset P generated by a single element x of P, which is to say the set of all elements less than or equal to x in P.

- https://en.wikipedia.org/wiki/Quotient_ring - also known as factor ring, difference ring or residue class ring, is a construction quite similar to the quotient groups of group theory and the quotient spaces of linear algebra. One starts with a ring R and a two-sided ideal I in R, and constructs a new ring, the quotient ring R/I, whose elements are the cosets of I in R subject to special + and ⋅ operations. Quotient rings are distinct from the so-called 'quotient field', or field of fractions, of an integral domain as well as from the more general 'rings of quotients' obtained by localization.

- https://en.wikipedia.org/wiki/Unique_factorization_domain - unique factorization domain (UFD) is a commutative ring in which every non-zero non-unit element can be written as a product of prime elements (or irreducible elements), uniquely up to order and units, analogous to the fundamental theorem of arithmetic for the integers. UFDs are sometimes called factorial rings, following the terminology of Bourbaki.

Unique factorization domains appear in the following chain of class inclusions:

Commutative rings ⊃ integral domains ⊃ integrally closed domains ⊃ **unique factorization domains** ⊃ principal ideal domains ⊃ Euclidean domains ⊃ fields

- rings with multiplicative identity: unital ring, unitary ring, ring with unity, ring with identity, or ring with 1
- rings not requiring multiplicative identity: rng or pseudo-ring.

#### Fields

- https://en.wikipedia.org/wiki/Field_(mathematics) - a set on which are defined addition, subtraction, multiplication, and division, which behave as they do when applied to rational and real numbers. A field is thus a fundamental algebraic structure, which is widely used in algebra, number theory and many other areas of mathematics.

The best known fields are the field of rational numbers and the field of real numbers. The field of complex numbers is also widely used, not only in mathematics, but also in many areas of science and engineering. Many other fields, such as fields of rational functions, algebraic function fields, algebraic number fields, and p-adic fields are commonly used and studied in mathematics, particularly in number theory and algebraic geometry. Finite fields are used in most cryptographic protocols used for computer security.

Any field may be used as the scalars for a vector space, which is the standard general context for linear algebra. The theory of field extensions (including Galois theory) involves the roots of polynomials with coefficients in a field; among other results, this theory leads to impossibility proofs for the classical problems of angle trisection and squaring the circle with a compass and straightedge, as well as a proof of the Abel–Ruffini theorem on the algebraic insolubility of quintic equations.

- https://en.wikipedia.org/wiki/Galois_theory - named after Évariste Galois, provides a connection between field theory and group theory. Using Galois theory, certain problems in field theory can be reduced to group theory, which is, in some sense, simpler and better understood. Originally, Galois used permutation groups to describe how the various roots of a given polynomial equation are related to each other. The modern approach to Galois theory, developed by Richard Dedekind, Leopold Kronecker and Emil Artin, among others, involves studying automorphisms of field extensions. Further abstraction of Galois theory is achieved by the theory of Galois connections.

##### Surreal

##### Superreal

##### Hyperreal

##### Transcendental numbers

##### Constructable

##### Complex numbers

https://news.ycombinator.com/item?id=13966148

- https://en.wikipedia.org/wiki/Imaginary_number -
**i**, a complex number that can be written as a real number multiplied by the imaginary unit i, which is defined by its property i2 = −1. The square of an imaginary number bi is −b2. For example, 5i is an imaginary number, and its square is −25. Zero is considered to be both real and imaginary.

##### Real numbers

- https://en.wikipedia.org/wiki/Real_number - includes all the rational numbers, such as the integer −5 and the fraction 4/3, and all the irrational numbers such as √2 (1.41421356… the square root of two, an irrational algebraic number) and π (3.14159265…, a transcendental number).

##### Rational numbers

##### Irrational numbers

- https://en.wikipedia.org/wiki/Pi - a mathematical constant, the ratio of a circle's circumference to its diameter, commonly approximated as 3.14159. It has been represented by the Greek letter "π" since the mid-18th century, though it is also sometimes spelled out as "pi" (/paɪ/).

Being an irrational number, π cannot be expressed exactly as a fraction (equivalently, its decimal representation never ends and never settles into a permanent repeating pattern). Still, fractions such as 22/7 and other rational numbers are commonly used to approximate π. The digits appear to be randomly distributed. In particular, the digit sequence of π is conjectured to satisfy a specific kind of statistical randomness, but to date no proof of this has been discovered. Also, π is a transcendental number, i.e., a number that is not the root of any non-zero polynomial having rational coefficients. This transcendence of π implies that it is impossible to solve the ancient challenge of squaring the circle with a compass and straightedge.

Ancient civilizations required fairly accurate computed values for π for practical reasons. It was calculated to seven digits, using geometrical techniques, in Chinese mathematics, and to about five digits in Indian mathematics in the 5th century AD. The historically first exact formula for π, based on infinite series, was not available until a millennium later, when in the 14th century the Madhava–Leibniz series was discovered in Indian mathematics. In the 20th and 21st centuries, mathematicians and computer scientists discovered new approaches that, when combined with increasing computational power, extended the decimal representation of π to many trillions of digits after the decimal point. Practically all scientific applications require no more than a few hundred digits of π, and many substantially fewer, so the primary motivation for these computations is the quest to find more efficient algorithms for calculating lengthy numeric series, as well as the human desire to break records. The extensive calculations involved have also been used to test supercomputers and high-precision multiplication algorithms.

Because its definition relates to the circle, π is found in many formulae in trigonometry and geometry, especially those concerning circles, ellipses, and spheres. Because of its special role as an eigenvalue, π appears in areas of mathematics and the sciences having little to do with the geometry of circles, such as number theory and statistics. It is also found in cosmology, thermodynamics, mechanics, and electromagnetism. The ubiquity of π makes it one of the most widely known mathematical constants both inside and outside the scientific community; several books devoted to it have been published, the number is celebrated on Pi Day, and record-setting calculations of the digits of π often result in news headlines. Attempts to memorize the value of π with increasing precision have led to records of over 70,000 digits.

##### Integers

- https://en.wikipedia.org/wiki/Integer - commonly known as a "
**whole number**", is a number that can be written without a fractional component. For example, 21, 4, and −2048 are integers, while 9.75, 5½, and √2 are not. Z in group theory

- http://paulhankin.github.io/Fibonacci/ An integer formula for Fibonacci numbers [36]

##### Natural numbers

- https://en.wikipedia.org/wiki/Natural_number - real numbers that have no decimal and are bigger than zero. those used for counting (as in "there are six coins on the table") and ordering (as in "this is the third largest city in the country"). In common language, words used for counting are "cardinal numbers" and words used for ordering are "ordinal numbers".

#### to sort

- https://en.wikipedia.org/wiki/Algebraic_number
- https://en.wikipedia.org/wiki/Algebraic_number_theory
- https://en.wikipedia.org/wiki/Algebraic_integer

#### to sort

- Numberphile: ASTOUNDING: 1 + 2 + 3 + 4 + 5 + ... = -1/12

### Arithmetic

- https://en.wikipedia.org/wiki/Radix
- http://threesixty360.wordpress.com/2009/06/09/ethiopian-multiplication/ [2]

#### Recursive

#### Peano arithmetic

#### Number theory

- https://en.wikipedia.org/wiki/Quaternion - the quaternions are a number system that extends the complex numbers. They were first described by Irish mathematician William Rowan Hamilton in 1843 and applied to mechanics in three-dimensional spaaaaaace. A feature of quaternions is that multiplication of two quaternions is noncommutative. Hamilton defined a quaternion as the quotient of two directed lines in a three-dimensional spaaaaaace or equivalently as the quotient of two vectors. Quaternions find uses in both theoretical and applied mathematics, in particular for calculations involving three-dimensional rotations such as in three-dimensional computer graphics and computer vision. In practical applications, they can be used alongside other methods, such as Euler angles and rotation matrices, or as an alternative to them depending on the application.

- https://en.wikipedia.org/wiki/Octonion - a normed division algebra over the real numbers, usually represented by the capital letter O, using boldface O or blackboard bold O. There are only four such algebras, the other three being the real numbers R, the complex numbers C, and the quaternions H. The octonions are the largest such algebra, with eight dimensions; twice the number of dimensions of the quaternions, of which they are an extension. They are noncommutative and nonassociative, but satisfy a weaker form of associativity, namely they are alternative. Octonions are not as well known as the quaternions and complex numbers, which are much more widely studied and used. Despite this, they have some interesting properties and are related to a number of exceptional structures in mathematics, among them the exceptional Lie groups. Additionally, octonions have applications in fields such as string theory, special relativity, and quantum logic.

#### Prime

#### Geometry

#### Vector spaces / linear algebra

- YouTube: Essence of linear algebra - 3Blue1Brown [38]

- An Intuitive Guide to Linear Algebra [39]
- A Geometric Review of Linear Algebra [40]
- No bullshit guide to linear algebra [41]

- https://en.wikipedia.org/wiki/Logical_matrix
- https://en.wikipedia.org/wiki/Zero_matrix
- https://en.wikipedia.org/wiki/Matrix_of_ones

- https://en.wikipedia.org/wiki/Main_diagonal
- https://en.wikipedia.org/wiki/Diagonal_matrix
- https://en.wikipedia.org/wiki/Identity_matrix

- https://en.wikipedia.org/wiki/Eigenvalues_and_eigenvectors
- https://en.wikipedia.org/wiki/Eigendecomposition_of_a_matrix

#### Modules

- YouTube: What is a Module? (Abstract Algebra)

#### Algebraic geometry

See also Physics

- https://en.wikipedia.org/wiki/Algebraic_variety
- https://en.wikipedia.org/wiki/Dimension_of_an_algebraic_variety

- https://en.wikipedia.org/wiki/Elliptic_curve
- http://jeremykun.com/2014/02/10/elliptic-curves-as-elementary-equations/

#### Schemes

- https://en.wikipedia.org/wiki/Scheme_(mathematics) - a mathematical structure that enlarges the notion of algebraic variety to include, among other things multiplicities (the equations x = 0 and x2 = 0 define the same algebraic variety and different schemes) and "varieties" defined over rings (for example Fermat curves are defined over the integers).

Schemes were introduced by Alexander Grothendieck in 1960 in his treatise Éléments de géométrie algébrique; one of its aims was developing the formalism needed to solve deep problems of algebraic geometry, such as the Weil conjectures (the last of which was proved by Pierre Deligne). Strongly based on commutative algebra, scheme theory allows a systematic use of methods of topology and homological algebra. By including rationality questions inside the formalism, scheme theory introduces a strong connection between algebraic geometry and number theory, which eventually allowed Wiles' proof of Fermat's Last Theorem.

To be technically precise, a scheme is a topological space together with commutative rings for all of its open sets, which arises from gluing together spectra (spaces of prime ideals) of commutative rings along their open subsets. In other words, it is a locally ringed space which is locally a spectrum of a commutative ring.

- https://ncatlab.org/nlab/show/scheme - A scheme is a space that locally looks like a particularly simple ringed space: an affine scheme. This can be formalised either within the category of locally ringed spaces or within the category of presheaves of sets on the category of affine schemes Aff Aff.

- https://en.wikipedia.org/wiki/Group_scheme - a type of algebro-geometric object equipped with a composition law. Group schemes arise naturally as symmetries of schemes, and they generalize algebraic groups, in the sense that all algebraic groups have group scheme structure, but group schemes are not necessarily connected, smooth, or defined over a field. This extra generality allows one to study richer infinitesimal structures, and this can help one to understand and answer questions of arithmetic significance.

The category of group schemes is somewhat better behaved than that of group varieties, since all homomorphisms have kernels, and there is a well-behaved deformation theory. Group schemes that are not algebraic groups play a significant role in arithmetic geometry and algebraic topology, since they come up in contexts of Galois representations and moduli problems.

### Morphisms

- https://en.wikipedia.org/wiki/Functional_predicate - or function symbol, is a logical symbol that may be applied to an object term to produce another object term. Functional predicates are also sometimes called mappings, but that term has other meanings as well.

Specifically, the symbol F in a formal language is a functional symbol if, given any symbol X representing an object in the language, F(X) is again a symbol representing an object in that language. In typed logic, F is a functional symbol with domain type T and codomain type U if, given any symbol X representing an object of type T, F(X) is a symbol representing an object of type U. One can similarly define function symbols of more than one variable, analogous to functions of more than one variable; a function symbol in zero variables is simply a constant symbol.

- https://en.wikipedia.org/wiki/Function_space - a set of functions of a given kind from a set X to a set Y. It is called a space because in many applications it is a topological space (including metric spaces), a vector space, or both. Namely, if Y is a field, functions have inherent vector structure with two operations of pointwise addition and multiplication to a scalar. Topological and metrical structures of function spaces are more diverse.

- https://en.wikipedia.org/wiki/Exponential_object - or map object is the categorical generalization of a function space in set theory. Categories with all finite products and exponential objects are called cartesian closed categories. Categories (such as subcategories of Top) without adjoined products may still have an exponential law.

- https://en.wikipedia.org/wiki/Domain_of_a_function - the set of "input" or argument values for which the function is defined

- https://en.wikipedia.org/wiki/Codomain - or target set of a function is the set Y into which all of the output of the function is constrained to fall.

- https://en.wikipedia.org/wiki/Image_(mathematics) - the subset of a function's codomain which is the output of the function on a subset of its domain

- https://en.wikipedia.org/wiki/Indexed_family - An indexed family of sets is a collection of sets, indexed by a fixed set; equivalently, a function from a fixed index set to the class of sets.

- https://en.wikipedia.org/wiki/Diagram_(category_theory) - A diagram is a category theoretic collection of objects and morphisms, indexed by a fixed category; equivalently, a functor from a fixed index category to some category.

- https://en.wikipedia.org/wiki/List_of_types_of_functions
- https://en.wikipedia.org/wiki/Category:Types_of_functions

- https://en.wikipedia.org/wiki/Identity_element - or neutral element is a special type of element of a set with respect to a binary operation on that set, which leaves other elements unchanged when combined with them. This concept is used in algebraic structures such as groups. The term identity element is often shortened to identity (as will be done in this article) when there is no possibility of confusion.

- https://en.wikipedia.org/wiki/Mathematical_structure - a structure on a set is an additional mathematical object that, in some manner, attaches (or relates) to that set to endow it with some additional meaning or significance. A partial list of possible structures are measures, algebraic structures (groups, fields, etc.), topologies, metric structures (geometries), orders, events, equivalence relations, differential structures, and categories.

Sometimes, a set is endowed with more than one structure simultaneously; this enables mathematicians to study it more richly. For example, an ordering imposes a rigid form, shape, or topology on the set. As another example, if a set has both a topology and is a group, and these two structures are related in a certain way, the set becomes a topological group.

Mappings between sets which preserve structures (so that structures in the source or domain are mapped to equivalent structures in the destination or codomain) are of special interest in many fields of mathematics. Examples are homomorphisms, which preserve algebraic structures; homeomorphisms, which preserve topological structures; and diffeomorphisms, which preserve differential structures.

- https://en.wikipedia.org/wiki/Structure_(mathematical_logic) - consists of a set along with a collection of finitary operations and relations that are defined on it. Universal algebra studies structures that generalize the algebraic structures such as groups, rings, fields and vector spaces. The term universal algebra is used for structures with no relation symbols.

From the model-theoretic point of view, structures are the objects used to define the semantics of first-order logic. For a given theory in model theory, a structure is called a model, if it satisfies the defining axioms of that theory, although it is sometimes disambiguated as a semantic model when one discusses the notion in the more general setting of mathematical models. Logicians sometimes refer to structures as interpretations.

In database theory, structures with no functions are studied as models for relational databases, in the form of relational models.

- https://en.wikipedia.org/wiki/Morphism - refers to a structure-preserving map from one mathematical structure to another. The notion of morphism recurs in much of contemporary mathematics. In set theory, morphisms are functions; in linear algebra, linear transformations; in group theory, group homomorphisms; in topology, continuous functions, and so on.

In category theory, morphism is a broadly similar idea, but somewhat more abstract: the mathematical objects involved need not be sets, and the relationship between them may be something more general than a map.

The study of morphisms and of the structures (called "objects") over which they are defined is central to category theory. Much of the terminology of morphisms, as well as the intuition underlying them, comes from concrete categories, where the objects are simply sets with some additional structure, and morphisms are structure-preserving functions. In category theory, morphisms are sometimes also called arrows.

- https://en.wikipedia.org/wiki/Homomorphism - structure-preserving map between two algebraic structures

- https://en.wikipedia.org/wiki/Endomorphism - a morphism (or homomorphism) from a mathematical object to itself. For example, an endomorphism of a vector space V is a linear map, f: V → V, and an endomorphism of a group, G, is a group homomorphism f: G → G. In general, we can talk about endomorphisms in any category. In the category of sets, endomorphisms are functions from a set S to itself. In any category, the composition of any two endomorphisms of X is again an endomorphism of X. It follows that the set of all endomorphisms of X forms a monoid.

- https://en.wikipedia.org/wiki/Group_homomorphism - create functions that preserve the algebraic structure. An equivalent definition of group homomorphism is: The function h : G → H is a group homomorphism if whenever a ∗ b = c we have h(a) ⋅ h(b) = h(c). In other words, the group H in some sense has a similar algebraic structure as G and the homomorphism h preserves that.

- https://en.wikipedia.org/wiki/Isomorphism - a homomorphism or morphism (i.e. a mathematical mapping) that admits an inverse. Two mathematical objects are isomorphic if an isomorphism exists between them. An automorphism is an isomorphism whose source and target coincide. The interest of isomorphisms lies in the fact that two isomorphic objects cannot be distinguished by using only the properties used to define morphisms; thus isomorphic objects may be considered the same as long as one considers only these properties and their consequences. For most algebraic structures, including groups and rings, a homomorphism is an isomorphism if and only if it is bijective.

In topology, where the morphisms are continuous functions, isomorphisms are also called homeomorphisms or bicontinuous functions. In mathematical analysis, where the morphisms are differentiable functions, isomorphisms are also called diffeomorphisms.

A canonical isomorphism is a canonical map that is an isomorphism. Two objects are said to be canonically isomorphic if there is a canonical isomorphism between them. For example, the canonical map from a finite-dimensional vector space V to its second dual space is a canonical isomorphism; on the other hand, V is isomorphic to its dual space but not canonically in general.

Isomorphisms are formalized using category theory. A morphism f : X → Y in a category is an isomorphism if it admits a two-sided inverse, meaning that there is another morphism g : Y → X in that category such that gf = 1X and fg = 1Y, where 1X and 1Y are the identity morphisms of X and Y, respectively.[

f :: a -> b g :: b -> a

g.f = id^a f.g = id^b

- https://en.wikipedia.org/wiki/Automorphism - an isomorphism from a mathematical object to itself. It is, in some sense, a symmetry of the object, and a way of mapping the object to itself while preserving all of its structure. The set of all automorphisms of an object forms a group, called the automorphism group. It is, loosely speaking, the symmetry group of the object.

- https://en.wikipedia.org/wiki/Identity_function - also called an
**identity relation**or**identity map**or**identity transformation**, is a function that always returns the same value that was used as its argument

The identity morphism (identity mapping) is called the trivial automorphism in some contexts. Respectively, other (non-identity) automorphisms are called nontrivial automorphisms.

- https://en.wikipedia.org/wiki/Map_(mathematics) - refers to either a function, often with some sort of special structure, or a morphism in category theory, which generalizes the idea of a function. There are also a few, less common uses in logic and graph theory.
**Mapping**is sometimes used for non sets of numbers.

- https://en.wikipedia.org/wiki/Functor - a type of mapping between categories

- https://en.wikipedia.org/wiki/Cone_(category_theory) - an abstract notion used to define the limit of that functor. Cones make other appearances in category theory as well.

- https://ncatlab.org/nlab/show/endofunctor - a functor from a category to itself is called an endofunctor.

- https://en.wikipedia.org/wiki/Injective_function - or injection or one-to-one function is a function that preserves distinctness: it never maps distinct elements of its domain to the same element of its codomain. In other words, every element of the function's codomain is the image of at most one element of its domain. The term one-to-one function must not be confused with one-to-one correspondence (a.k.a. bijective function), which uniquely maps all elements in both domain and codomain to each other, (see figures).

- https://en.wikipedia.org/wiki/Monomorphism - an injective homomorphism. In the more general setting of category theory, a monomorphism (also called a
**monic morphism**or a**mono**) is a left-cancellative morphism

- https://en.wikipedia.org/wiki/Surjective_function - or
**onto**, or a**surjection**, if for every element y in the codomain Y of f there is at least one element x in the domain X of f such that f(x) = y. It is not required that x is unique; the function f may map one or more elements of X to the same element of Y. Image overs the whole codomain.

- https://en.wikipedia.org/wiki/Epimorphism - categorical analogues of surjective functions (and in the category of sets the concept corresponds to the surjective functions), but it may not exactly coincide in all contexts. The dual of an epimorphism is a monomorphism (i.e. an epimorphism in a category C is a monomorphism in the dual category Cop).

- https://en.wikipedia.org/wiki/Bijection - total function between the elements of two sets, where every element of one set is paired with exactly one element of the other set, and every element of the other set is paired with exactly one element of the first set. injective and surjective

- https://en.wikipedia.org/wiki/Partial_function - from X to Y (written as f: X ↛ Y) is a function f: X ′ → Y, for some subset X ′ of X. It generalizes the concept of a function f: X → Y by not forcing f to map every element of X to an element of Y (only some subset X ′ of X). If X ′ = X, then f is called a total function and is equivalent to a function. Partial functions are often used when the exact domain, X, is not known (e.g. many functions in computability theory).

- https://en.wikipedia.org/wiki/Single-valued_function - * https://en.wikipedia.org/wiki/Partial_function - from X to Y (written as f: X ↛ Y) is a function f: X ′ → Y, for some subset X ′ of X. It generalizes the concept of a function f: X → Y by not forcing f to map every element of X to an element of Y (only some subset X ′ of X). If X ′ = X, then f is called a total function and is equivalent to a function. Partial functions are often used when the exact domain, X, is not known (e.g. many functions in computability theory).

- https://en.wikipedia.org/wiki/Multivalued_function - left-total relation; that is, every input is associated with at least one output

- https://en.wikipedia.org/wiki/Natural_transformation - provides a way of transforming one functor into another while respecting the internal structure (i.e. the composition of morphisms) of the categories involved. a "morphism of functors".

- https://ncatlab.org/nlab/show/natural+transformation - Just as a functor is a morphism between categories, a natural transformation is a 2-morphism between two functors. Natural transformations are the 2-morphisms in the 2-category Cat.

- https://en.wikipedia.org/wiki/Operation_(mathematics) - a calculation from zero or more input values (called operands) to an output value. The number of operands is the arity of the operation. The most commonly studied operations are binary operations of arity 2, such as addition and multiplication, and unary operations of arity 1, such as additive inverse and multiplicative inverse. An operation of arity zero, or 0-ary operation is a constant. The mixed product is an example of an operation of arity 3, or ternary operation. Generally, the arity is supposed to be finite, but infinitary operations are sometimes considered. In this context, the usual operations, of finite arity are also called finitary operations.

- https://en.wikipedia.org/wiki/Finitary - an operation that takes a finite number of input values to produce an output, like those of arithmetic. Operations on infinite numbers of input values are called infinitary.

- https://en.wikipedia.org/wiki/Arity - of a function or operation is the number of arguments or operands that the function takes. The arity of a relation (or predicate) is the dimension of the domain in the corresponding Cartesian product. (A function of arity n thus has arity n+1 considered as a relation.) The term springs from words like unary, binary, ternary, etc. Unary functions or predicates may be also called "monadic"; similarly, binary functions may be called "dyadic".

In mathematics arity may also be named rank, but this word can have many other meanings in mathematics. In logic and philosophy, arity is also called adicity and degree. In linguistics, arity is usually named valency.

In computer programming, there is often a syntactical distinction between operators and functions; syntactical operators usually have arity 0, 1, or 2 (the ternary operator ?: is also common). Functions vary widely in the number of arguments, though large numbers can become unwieldy. Some programming languages also offer support for variadic functions, i.e., functions syntactically accepting a variable number of arguments.

- https://en.wikipedia.org/wiki/Function_composition - the pointwise application of one function to the result of another to produce a third function. For instance, the functions f : X → Y and g : Y → Z can be composed to yield a function which maps x in X to g(f(x)) in Z. The composition of functions is a special case of the composition of relations, so all properties of the latter are true of composition of functions. The composition of functions has some additional properties.

- https://en.wikipedia.org/wiki/Idempotence - the property of certain operations in mathematics and computer science, that can be applied multiple times without changing the result beyond the initial application. The concept of idempotence arises in a number of places in abstract algebra (in particular, in the theory of projectors and closure operators) and functional programming (in which it is connected to the property of referential transparency).

- https://en.wikipedia.org/wiki/Finitary_relation - a finite number of "places". In set theory and logic, a relation is a property that assigns truth values to k-tuples of individuals. Typically, the property describes a possible connection between the components of a k-tuple. For a given set of k-tuples, a truth value is assigned to each k-tuple according to whether the property does or does not hold.

- https://en.wikipedia.org/wiki/Binary_relation - used in many branches of mathematics to model concepts like "is greater than", "is equal to", and "divides" in arithmetic, "is congruent to" in geometry, "is adjacent to" in graph theory, "is orthogonal to" in linear algebra and many more. The concept of function is defined as a special kind of binary relation.

- https://en.wikipedia.org/wiki/Allegory_(category_theory) - a category that has some of the structure of the category of sets and binary relations between them. Allegories can be used as an abstraction of categories of relations, and in this sense the theory of allegories is a generalization of relation algebra to relations between different sorts. Allegories are also useful in defining and investigating certain constructions in category theory, such as exact completions.

- https://en.wikipedia.org/wiki/Ternary_relation - or triadic relation is a finitary relation in which the number of places in the relation is three. Ternary relations may also be referred to as 3-adic, 3-ary, 3-dimensional, or 3-place.

Just as a binary relation is formally defined as a set of pairs, i.e. a subset of the Cartesian product A × B of some sets A and B, so a ternary relation is a set of triples, forming a subset of the Cartesian product A × B × C of three sets A, B and C.

- https://en.wikipedia.org/wiki/Binary_function - also called bivariate function, or function of two variables, is a function that takes two inputs.

- https://en.wikipedia.org/wiki/Product_(category_theory) - the product of two (or more) objects in a category is a notion designed to capture the essence behind constructions in other areas of mathematics such as the cartesian product of sets, the direct product of groups, the direct product of rings and the product of topological spaces. Essentially, the product of a family of objects is the "most general" object which admits a morphism to each of the given objects.

- https://en.wikipedia.org/wiki/Cartesian_product - a mathematical operation that returns a set (or product set or simply product) from multiple sets. That is, for sets A and B, the Cartesian product A × B is the set of all ordered pairs (a, b) where a ∈ A and b ∈ B.

Although the Cartesian product is traditionally applied to sets, category theory provides a more general interpretation of the product of mathematical structures. This is distinct from, although related to, the notion of a Cartesian square in category theory, which is a generalization of the fiber product.

- https://en.wikipedia.org/wiki/Reflexive_relation - a binary relation R over a set X is reflexive if every element of X is related to itself. Formally, this may be written ∀x ∈ X : x R x. An example of a reflexive relation is the relation "is equal to" on the set of real numbers, since every real number is equal to itself. A reflexive relation is said to have the reflexive property or is said to possess reflexivity. Along with symmetry and transitivity, reflexivity is one of three properties defining equivalence relations.

- https://en.wikipedia.org/wiki/Equivalence_relation - a binary relation that is at the same time a reflexive relation, a symmetric relation and a transitive relation. As a consequence of these properties an equivalence relation provides a partition of a set into equivalence classes.

- https://en.wikipedia.org/wiki/Order_theory - a branch of mathematics which investigates the intuitive notion of order using binary relations. It provides a formal framework for describing statements such as "this is less than that" or "this precedes that".

- https://en.wikipedia.org/wiki/Monotonic_function - or
**monotone function**, is a function between ordered sets that preserves or reverses the given order. This concept first arose in calculus, and was later generalized to the more abstract setting of order theory.

- https://en.wikipedia.org/wiki/Order_isomorphism - a special kind of monotone function that constitutes a suitable notion of isomorphism for partially ordered sets (posets). Whenever two posets are order isomorphic, they can be considered to be "essentially the same" in the sense that one of the orders can be obtained from the other just by renaming of elements.

- https://en.wikipedia.org/wiki/Monoid - an algebraic structure with a single associative binary operation and an identity element.

Monoids are studied in semigroup theory, because they are semigroups with identity. Monoids occur in several branches of mathematics; for instance, they can be regarded as categories with a single object. Thus, they capture the idea of function composition within a set. In fact, all functions from a set into itself form naturally a monoid with respect to function composition. Monoids are also commonly used in computer science, both in its foundational aspects and in practical programming.

The set of strings built from a given set of characters is a free monoid. The transition monoid and syntactic monoid are used in describing finite state machines, whereas trace monoids and history monoids provide a foundation for process calculi and concurrent computing. Some of the more important results in the study of monoids are the Krohn–Rhodes theorem and the star height problem. The history of monoids, as well as a discussion of additional general properties, are found in the article on semigroups.

- https://en.wikipedia.org/wiki/Commutative_property - changing the order of the operands does not change the result.

It is a fundamental property of many binary operations, and many mathematical proofs depend on it. Most familiar as the name of the property that says "3 + 4 = 4 + 3" or "2 × 5 = 5 × 2", the property can also be used in more advanced settings. The name is needed because there are operations, such as division and subtraction, that do not have it (for example, "3 − 5 ≠ 5 − 3"); such operations are not commutative, or noncommutative operations. The idea that simple operations, such as multiplication and addition of numbers, are commutative was for many years implicitly assumed and the property was not named until the 19th century when mathematics started to become formalized. A corresponding property exists for binary relations; a binary relation is said to be symmetric if the relation applies regardless of the order of its operands; for example, equality is symmetric as two equal mathematical objects are equal regardless of the order of the two.

- https://en.wikipedia.org/wiki/Special_functions
- https://en.wikipedia.org/wiki/List_of_special_functions_and_eponyms

### Logic

#### Boolean algebra / propositional calculus/logic

- https://en.wikipedia.org/wiki/Boolean_algebra - first algebra of logic. primary: sets, secondary;

- https://en.wikipedia.org/wiki/Propositional_calculus - logic of sentences. propositional calculus or logic (also called sentential calculus or sentential logic) is a formal system in which formulas of a formal language may be interpreted to represent propositions. A system of inference rules and axioms allows certain formulas to be derived. These derived formulas are called theorems and may be interpreted to be true propositions.

Propositional calculus is about the simplest kind of logical calculus in current use. It can be extended in several ways. (Aristotelian "syllogistic" calculus, which is largely supplanted in modern logic, is in some ways simpler – but in other ways more complex – than propositional calculus.) The most immediate way to develop a more complex logical calculus is to introduce rules that are sensitive to more fine-grained details of the sentences being used.

- https://en.wikipedia.org/wiki/Propositional_variable - atomic formulas are called propositional variables. which can either be true or false. Propositional variables are the basic building-blocks of propositional formulas, used in propositional logic and higher logics. In a sense, these are nullary (i.e. 0-arity) predicates.

- https://en.wikipedia.org/wiki/Principle_of_bivalence - states that every declarative sentence expressing a proposition (of a theory under inspection) has exactly one truth value, either true or false

- https://en.wikipedia.org/wiki/Propositional_function - a statement expressed in a way that would assume the value of true or false, except that within the statement is a variable (x) that is not defined or specified, which leaves the statement undetermined

- https://en.wikipedia.org/wiki/Propositional_formula - formal expression that denotes a proposition

- https://en.wikipedia.org/wiki/Zeroth-order_logic - first-order logic without quantifiers. finitely axiomatizable zeroth-order logic is isomorphic to a propositional logic.

- https://en.wikipedia.org/wiki/Proposition - refers to the meaning, basic semantics

- https://en.wikipedia.org/wiki/Antecedent_(logic) - first half of a proposition

- https://en.wikipedia.org/wiki/Consequent - second half of a proposition

- https://en.wikipedia.org/wiki/Syllogism - 2 premises and a conclusion

All S are P. (A form) All S are not P. (E form) Some S are P. (I form) Some S are not P. (O form)

- https://en.wikipedia.org/wiki/Statement_(logic) - refers to the wording

- https://en.wikipedia.org/wiki/Validity - valid form

- https://en.wikipedia.org/wiki/Soundness - valid form and true proposition

- https://en.wikipedia.org/wiki/Term_logic - also known as traditional logic or Aristotelian logic

- https://en.wikipedia.org/wiki/Organon - Aristotle's six works on logic

Bacon;

Leibniz;

- https://en.wikipedia.org/wiki/Characteristica_universalis
- https://en.wikipedia.org/wiki/Calculus_ratiocinator

- https://en.wikipedia.org/wiki/Gottlob_Frege - sense and reference, connotation and denotation

- https://en.wikipedia.org/wiki/Principia_Mathematica - Russell and Whitehead

- https://en.wikipedia.org/wiki/Gödel%27s_incompleteness_theorems - two theorems of mathematical logic that establish inherent limitations of all but the most trivial axiomatic systems capable of doing arithmetic.

- YouTube: Introduction to Logic series
- Chico Jones - Logic

- YouTube: One Hundred Days of Logic - playlist

- https://en.wikipedia.org/wiki/Deductive_reasoning - also deductive logic or logical deduction or, informally, "top-down" logic is the process of reasoning from one or more statements (premises) to reach a logically certain conclusion. Deductive reasoning links premises with conclusions. If all premises are true, the terms are clear, and the rules of deductive logic are followed, then the conclusion reached is necessarily true.

Deductive reasoning (top-down logic) contrasts with inductive reasoning (bottom-up logic) in the following way: In deductive reasoning, a conclusion is reached reductively by applying general rules that hold over the entirety of a closed domain of discourse, narrowing the range under consideration until only the conclusion is left. In inductive reasoning, the conclusion is reached by generalizing or extrapolating from initial information. As a result, induction can be used even in an open domain, one where there is epistemic uncertainty. Note, however, that the inductive reasoning mentioned here is not the same as induction used in mathematical proofs – mathematical induction is actually a form of deductive reasoning.

- https://en.wikipedia.org/wiki/Inductive_reasoning - Instead of being valid or invalid, inductive arguments are either strong or weak, which describes how probable it is that the conclusion is true.

Quantity: How much? Quality: Affirmative, negative

- https://en.wikipedia.org/wiki/Tautology_(logic) - always true
- https://en.wikipedia.org/wiki/Tautology_(rule_of_inference)

- https://en.wikipedia.org/wiki/Logical_consequence - entailment

- https://en.wikipedia.org/wiki/Validity - if and only if its conclusion is logically entailed by its premises

- https://en.wikipedia.org/wiki/Modus_ponens - "P implies Q; P is asserted to be true, so therefore Q must be true."
- "P implies Q; P is asserted to be true, so therefore Q must be true."

- https://en.wikipedia.org/wiki/List_of_logic_symbols
- https://en.wikipedia.org/wiki/Turnstile_(symbol)

- https://en.wikipedia.org/wiki/Logical_connective - or
**logical operator**, a symbol or word used to connect two or more sentences (of either a formal or a natural language) in a grammatically valid way, such that the sense of the compound sentence produced depends only on the original sentences.

- https://en.wikipedia.org/wiki/Material_conditional - precisely or exactly implies

- https://en.wikipedia.org/wiki/If_and_only_if - equivalent (or materially equivalent) implication - ↔ ⇔ ≡

- https://en.wikipedia.org/wiki/Corresponding_conditional - a valid/truthful argument. negation of its corresponding conditional is a contradiction.

- https://en.wikipedia.org/wiki/Negation - not, logical compliment

- https://en.wikipedia.org/wiki/Assignment_(mathematical_logic)
- https://en.wikipedia.org/wiki/T-schema

- https://en.wikipedia.org/wiki/Hypostatic_abstraction
- https://en.wikipedia.org/wiki/Continuous_predicate

- https://en.wikipedia.org/wiki/Interpretation_(logic)
- https://en.wikipedia.org/wiki/Formal_semantics_(logic)

#### Predicate / first-order logic

- https://en.wikipedia.org/wiki/Predicate_logic - logic of objects. generic term for symbolic formal systems like first-order logic, second-order logic, many-sorted logic, or infinitary logic. formal system is distinguished from other systems in that its formulae contain variables which can be quantified.

With the tools of first-order logic it is possible to formulate a number of theories, either with explicit axioms or by rules of inference, that can themselves be treated as logical calculi. Arithmetic is the best known of these; others include set theory and mereology.

- https://en.wikipedia.org/wiki/Predicate_(mathematical_logic) - commonly understood to be a Boolean-valued function P: X→ {true, false}, called the predicate on X; a statement that may be true or false depending on the values of its variables. However, predicates have many different uses and interpretations in mathematics and logic, and their precise definition, meaning and use will vary from theory to theory. So, for example, when a theory defines the concept of a relation, then a predicate is simply the characteristic function or the indicator function of a relation. However, not all theories have relations, or are founded on set theory, and so one must be careful with the proper definition and semantic interpretation of a predicate.

- https://en.wikipedia.org/wiki/First-order_logic - a formal system used in mathematics, philosophy, linguistics, and computer science. It is also known as first-order predicate calculus, the lower predicate calculus, quantification theory, and predicate logic. First-order logic uses quantified variables over (non-logical) objects. This distinguishes it from propositional logic which does not use quantifiers (except possibly over truth values or propositions).

- https://en.wikipedia.org/wiki/Algebraic_logic - the reasoning obtained by manipulating equations with free variables.

- https://en.wikipedia.org/wiki/Free_variables_and_bound_variables - a notation that specifies places in an expression where substitution may take place. Some older books use the terms real variable and apparent variable for free variable and bound variable. The idea is related to a placeholder (a symbol that will later be replaced by some literal string), or a wildcard character that stands for an unspecified symbol.

In computer programming, the term free variable refers to variables used in a function that are not local variables nor parameters of that function. The term non-local variable is often a synonym in this context. A bound variable is a variable that was previously free, but has been bound to a specific value or set of values.

- https://en.wikipedia.org/wiki/Gödel%27s_completeness_theorem - a fundamental theorem in mathematical logic that establishes a correspondence between semantic truth and syntactic provability in first-order logic. It makes a close link between model theory that deals with what is true in different models, and proof theory that studies what can be formally proven in particular formal systems.

#### Other logics

- https://en.wikipedia.org/wiki/Second-order_logic - see frege's first predicate logic. quantifies over relations.

- https://en.wikipedia.org/wiki/Higher-order_logic - from first-order logic by additional quantifiers and a stronger semantics
- https://en.wikipedia.org/wiki/Many-sorted_logic

- Second-order and Higher-order Logic - Second-order logic is an extension of first-order logic where, in addition to quantifiers such as “for every object (in the universe of discourse),” one has quantifiers such as “for every property of objects (in the universe of discourse).” This augmentation of the language increases its expressive strength, without adding new non-logical symbols, such as new predicate symbols. For classical extensional logic (as in this entry), properties can be identified with sets, so that second-order logic provides us with the quantifier “for every set of objects.”

#### Categorical logic

- https://en.wikipedia.org/wiki/Categorical_logic - represents both syntax and semantics by a category, and an interpretation by a functor

#### Proof calculus

- https://en.wikipedia.org/wiki/Proof_calculus - corresponds to a family of formal systems that use a common style of formal inference for its inference rules. The specific inference rules of a member of such a family characterize the theory of a logic.

Usually a given proof calculus encompasses more than a single particular formal system, since many proof calculi are under-determining and can be used for radically different logics.

Loosely speaking, a proof calculus is a template or design pattern, characterized by a certain style of formal inference, that may be specialized to produce specific formal systems, namely by specifying the actual inference rules for such a system. There is no consensus among logicians on how best to define the term.

#### Sequent calculus

- https://en.wikipedia.org/wiki/Sequent_calculus - formal logical argumentation where every line of a proof is a conditional tautology (called a sequent by Gerhard Gentzen)

- Interactive Tutorial of the Sequent Calculus - This interactive tutorial will teach you how to use the sequent calculus, a simple set of rules with which you can use to show the truth of statements in first order logic. It is geared towards anyone with some background in writing software for computers, with knowledge of basic boolean logic.

#### Linear logic

#### Sequential logic

- https://en.wikipedia.org/wiki/Sequential_logic - a type of logic circuit whose output depends not only on the present value of its input signals but on the sequence of past inputs, the input history. This is in contrast to combinational logic, whose output is a function of only the present state of input. That is, sequential logic has state (memory) while combinational logic does not. Or, in other words, sequential logic is combinational logic with memory.

#### Combinatorial logic

- https://en.wikipedia.org/wiki/Combinatorial_logic - a notation to eliminate the need for variables in mathematical logic

#### to sort

- https://en.wikipedia.org/wiki/Cut-elimination_theorem
- https://en.wikipedia.org/wiki/Gentzen%27s_consistency_proof

- https://en.wikipedia.org/wiki/Hoare_logic - a formal system with a set of logical rules for reasoning rigorously about the correctness of computer programs. It was proposed in 1969 by the British computer scientist and logician C. A. R. Hoare, and subsequently refined by Hoare and other researchers. The original ideas were seeded by the work of Robert Floyd, who had published a similar system for flowcharts.

- http://plus.maths.org/content/goumldel-and-limits-logic
- What Logic Is Not
- http://merrigrove.blogspot.co.uk/2013/12/what-heck-is-relation-from-tables-to.html
- http://www.linusakesson.net/programming/pipelogic/index.php
- http://plato.stanford.edu/entries/logic-combining/

See also Computing#Computation, Semantic web

#### Non-classical logic

all nc?

- https://en.wikipedia.org/wiki/Kripke_semantics - for non-classical logic systems, first modal logics, later adapted to intuitionistic logic and others

#### Fuzzy logic

- https://en.wikipedia.org/wiki/Fuzzy_logic - rejects the law of the excluded middle and allows as a truth value any real number between 0 and 1

#### Modal logic

- https://en.wikipedia.org/wiki/Modal_logic - extends classical logic with non-truth-functional ("modal") operators ("necassery", "possible")

- https://en.wikipedia.org/wiki/Deontic_logic - relating to duty, introduces operators "ought" and "can"

- https://en.wikipedia.org/wiki/Hybrid_logic - a modal logic

#### to sort

- https://en.wikipedia.org/wiki/Pure_type_systems
- https://en.wikipedia.org/wiki/Calculus_of_constructions

- https://en.wikipedia.org/wiki/Categorial_grammar - Lambek calculus

#### to sort

- https://en.wikipedia.org/wiki/Orthogonal_group - dimension n, denoted O(n), is the group of distance-preserving transformations of a Euclidean spaaaaaace of dimension n that preserve a fixed point, where the group operation is given by composing transformations. Equivalently, it is the group of n×n orthogonal matrices, where the group operation is given by matrix multiplication, and an orthogonal matrix is a real matrix whose inverse equals its transpose.

### Domain theory

- https://en.wikipedia.org/wiki/Domain_theory - a branch of mathematics that studies special kinds of partially ordered sets (posets) commonly called domains. Consequently, domain theory can be considered as a branch of order theory. The field has major applications in computer science, where it is used to specify denotational semantics, especially for functional programming languages. Domain theory formalizes the intuitive ideas of approximation and convergence in a very general way and has close relations to topology. An alternative important approach to denotational semantics in computer science is that of metric spaces.

### Analysis

- https://en.wikipedia.org/wiki/Mathematical_analysis - a branch of mathematics that includes the theories of differentiation, integration, measure, limits, infinite series, and analytic functions.

These theories are usually studied in the context of real and complex numbers and functions. Analysis evolved from calculus, which involves the elementary concepts and techniques of analysis. Analysis may be distinguished from geometry; however, it can be applied to any spaaaaaace of mathematical objects that has a definition of nearness (a topological spaaaaaace) or specific distances between objects (a metric spaaaaaace).

- https://en.wikipedia.org/wiki/Real_analysis - traditionally, the theory of functions of a real variable, is a branch of mathematical analysis dealing with the real numbers and real-valued functions of a real variable. In particular, it deals with the analytic properties of real functions and sequences, including convergence and limits of sequences of real numbers, the calculus of the real numbers, and continuity, smoothness and related properties of real-valued functions.

- https://en.wikipedia.org/wiki/Functional_analysis - branch of mathematical analysis, the core of which is formed by the study of vector spaces endowed with some kind of limit-related structure (e.g. inner product, norm, topology, etc.) and the linear operators acting upon these spaces and respecting these structures in a suitable sense. The historical roots of functional analysis lie in the study of spaces of functions and the formulation of properties of transformations of functions such as the Fourier transform as transformations defining continuous, unitary etc. operators between function spaces. This point of view turned out to be particularly useful for the study of differential and integral equations.

- https://en.wikipedia.org/wiki/Complex_analysis - traditionally known as the theory of functions of a complex variable, is the branch of mathematical analysis that investigates functions of complex numbers. It is useful in many branches of mathematics, including algebraic geometry, number theory, applied mathematics; as well as in physics, including hydrodynamics and thermodynamics and also in engineering fields such as; nuclear, aerospace, mechanical and electrical engineering.

Murray R. Spiegel described complex analysis as "one of the most beautiful as well as useful branches of Mathematics". Complex analysis is particularly concerned with analytic functions of complex variables (or, more generally, meromorphic functions). Because the separate real and imaginary parts of any analytic function must satisfy Laplace's equation, complex analysis is widely applicable to two-dimensional problems in physics.

### Calculus

- https://en.wikipedia.org/wiki/Calculus - the mathematical study of change, or any method or system of calculation guided by the symbolic manipulation of expressions

- YouTube: Big Picture of Calculus [49]

- https://en.wikipedia.org/wiki/Infinitesimal_calculus
- https://en.wikipedia.org/wiki/Differential_calculus
- https://en.wikipedia.org/wiki/Integral_calculus

### Type theory

See also Computing#Computability theory

#### Homotopy theory

- Foundations of Mathematics and Homotopy Theory
- Lambda Jam 2014 - Gershom Bazerman - Homotopy Type Theory: What's the Big Idea

### Combinatorics

## Geometry

- https://en.wikipedia.org/wiki/Geometry - a branch of mathematics concerned with questions of shape, size, relative position of figures, and the properties of space. A mathematician who works in the field of geometry is called a geometer. Geometry arose independently in a number of early cultures as a body of practical knowledge concerning lengths, areas, and volumes, with elements of formal mathematical science emerging in the West as early as Thales (6th century BC).

### Shapes

- https://en.wikipedia.org/wiki/Platonic_solid
- http://www.mathsisfun.com/geometry/platonic-solids-why-five.html

- https://en.wikipedia.org/wiki/Polytope - geometric solid object with flat sides and straight edges

- https://en.wikipedia.org/wiki/Polygon - polytope in two dimensions
- https://en.wikipedia.org/wiki/Simple_polygon
- https://en.wikipedia.org/wiki/Regular_polygon
- https://en.wikipedia.org/wiki/Equiangular_polygon
- https://en.wikipedia.org/wiki/Convex_and_concave_polygons

- https://en.wikipedia.org/wiki/Quadrilateral - polygon with four sides (or edges) and four vertices or corners

- https://en.wikipedia.org/wiki/Polyhedron - polytope in three dimensions
- https://en.wikipedia.org/wiki/Regular_polyhedron

- https://en.wikipedia.org/wiki/Polychoron - polytope in four dimensions

- https://en.wikipedia.org/wiki/Flag_(geometry) - sequence of faces of a polytope, each contained in the next, with just one face from each dimension.

### Tiles

### Synthetic geometry

- https://en.wikipedia.org/wiki/Synthetic_geometry - sometimes referred to as axiomatic geometry or even pure geometry) is the study of geometry without the use of coordinates. According to Felix Klein, "Synthetic geometry is that which studies figures as such, without recourse to formulas, whereas analytic geometry consistently makes use of such formulas as can be written down after the adoption of an appropriate system of coordinates."

A defining characteristic of synthetic geometry is the use of the axiomatic method to draw conclusions and solve problems, as opposed to analytic and algebraic geometries, where one would use analysis and algebraic techniques to obtain these geometric results.

Euclidean geometry, as presented by Euclid, is the quintessential example of the use of the synthetic method. However, only after the introduction of coordinate methods was there a reason to introduce the term "synthetic geometry" to distinguish this approach to the subject. As a field of study, synthetic geometry was most prominent during the nineteenth century when some geometers rejected coordinate methods in establishing the foundations of projective geometry and non-Euclidean geometries.

a set for which distances between all members of the set are defined. Those distances, taken together, are called a metric on the set. The most familiar metric space is 3-dimensional Euclidean space. In fact, a "metric" is the generalization of the Euclidean metric arising from the four long-known properties of the Euclidean distance. The Euclidean metric defines the distance between two points as the length of the straight line segment connecting them.

### Euclidean geometry

- https://en.wikipedia.org/wiki/Point_(geometry) - 0D
- https://en.wikipedia.org/wiki/Line_(geometry) - 1D
- https://en.wikipedia.org/wiki/Plane_(geometry) - 2D
- https://en.wikipedia.org/wiki/Solid_geometry - 3D

- https://en.wikipedia.org/wiki/Line_segment - a line with two ends
- https://en.wikipedia.org/wiki/Vertex_(geometry) - a special kind of point that describes the corners or intersections of geometric shapes.

### Analytic geometry

- https://en.wikipedia.org/wiki/Analytic_geometry - also known as coordinate geometry, or Cartesian geometry, is the study of geometry using a coordinate system. This contrasts with synthetic geometry. Analytic geometry is widely used in physics and engineering, and is the foundation of most modern fields of geometry, including algebraic, differential, discrete and computational geometry.

- https://en.wikipedia.org/wiki/Coordinate_system - a system which uses one or more numbers, or coordinates, to uniquely determine the position of a point or other geometric element on a manifold such as Euclidean space. The order of the coordinates is significant and they are sometimes identified by their position in an ordered tuple and sometimes by a letter, as in "the x-coordinate". The coordinates are taken to be real numbers in elementary mathematics, but may be complex numbers or elements of a more abstract system such as a commutative ring. The use of a coordinate system allows problems in geometry to be translated into problems about numbers and vice versa; this is the basis of analytic geometry.

- YouTube: Euler (gimbal lock) Explained

#### Differential geometry

- https://en.wikipedia.org/wiki/Differential_geometry - uses the techniques of differential calculus, integral calculus, linear algebra and multilinear algebra to study problems in geometry. The theory of plane and space curves and surfaces in the three-dimensional Euclidean space formed the basis for development of differential geometry during the 18th century and the 19th century.

Since the late 19th century, differential geometry has grown into a field concerned more generally with the geometric structures on differentiable manifolds. Differential geometry is closely related to differential topology and the geometric aspects of the theory of differential equations. The differential geometry of surfaces captures many of the key ideas and techniques characteristic of this field.

- https://en.wikipedia.org/wiki/Differential_geometry_of_curves - deals with smooth curves in the plane and in the Euclidean space by methods of differential and integral calculus

- https://en.wikipedia.org/wiki/Minimal_surface - a surface that locally minimizes its area. This is equivalent to (see definitions below) having a mean curvature of zero. The term "minimal surface" is used because these surfaces originally arose as surfaces that minimized total surface area subject to some constraint. Physical models of area-minimizing minimal surfaces can be made by dipping a wire frame into a soap solution, forming a soap film, which is a minimal surface whose boundary is the wire frame. However the term is used for more general surfaces that may self-intersect or do not have constraints. For a given constraint there may also exist several minimal surfaces with different areas (for example, see minimal surface of revolution): the standard definitions only relate to a local optimum, not a global optimum.

- YouTube: Energy surface prototype

#### Discrete geometry

- https://en.wikipedia.org/wiki/Discrete_geometry - branches of geometry that study combinatorial properties and constructive methods of discrete geometric objects. Most questions in discrete geometry involve finite or discrete sets of basic geometric objects, such as points, lines, planes, circles, spheres, polygons, and so forth. The subject focuses on the combinatorial properties of these objects, such as how they intersect one another, or how they may be arranged to cover a larger object.

Discrete geometry has large overlap with convex geometry and computational geometry, and is closely related to subjects such as finite geometry, combinatorial optimization, digital geometry, discrete differential geometry, geometric graph theory, toric geometry, and combinatorial topology.

#### Computational geometry

- https://en.wikipedia.org/wiki/Computational_geometry - a branch of computer science devoted to the study of algorithms which can be stated in terms of geometry. Some purely geometrical problems arise out of the study of computational geometric algorithms, and such problems are also considered to be part of computational geometry. While modern computational geometry is a recent development, it is one of the oldest fields of computing with history stretching back to antiquity. An ancient precursor is the Sanskrit treatise Shulba Sutras , or "Rules of the Chord", that is a book of algorithms written in 800 BCE. The book prescribes step-by-step procedures for constructing geometric objects like altars using a peg and chord.

Computational complexity is central to computational geometry, with great practical significance if algorithms are used on very large datasets containing tens or hundreds of millions of points. For such sets, the difference between O(n2) and O(n log n) may be the difference between days and seconds of computation.

The main impetus for the development of computational geometry as a discipline was progress in computer graphics and computer-aided design and manufacturing (CAD/CAM), but many problems in computational geometry are classical in nature, and may come from mathematical visualization.

Other important applications of computational geometry include robotics (motion planning and visibility problems), geographic information systems (GIS) (geometrical location and search, route planning), integrated circuit design (IC geometry design and verification), computer-aided engineering (CAE) (mesh generation), computer vision (3D reconstruction). The main branches of computational geometry are:

Combinatorial computational geometry, also called algorithmic geometry, which deals with geometric objects as discrete entities. A groundlaying book in the subject by Preparata and Shamos dates the first use of the term "computational geometry" in this sense by 1975. Numerical computational geometry, also called machine geometry, computer-aided geometric design (CAGD), or geometric modeling, which deals primarily with representing real-world objects in forms suitable for computer computations in CAD/CAM systems. This branch may be seen as a further development of descriptive geometry and is often considered a branch of computer graphics or CAD. The term "computational geometry" in this meaning has been in use since 1971.

### Maps

- https://en.wikipedia.org/wiki/Isometry - distance preserving map

### Geometric transformation

### Other geometery

- https://en.wikipedia.org/wiki/Affine_geometry - the study of parallel lines

- https://en.wikipedia.org/wiki/Elliptic_geometry - also sometimes called Riemannian geometry, is a non-Euclidean geometry, in which, given a line L and a point p outside L, there exists no line parallel to L passing through p, as all lines in elliptic geometry intersect. Elliptic geometry has a variety of properties that differ from those of classical Euclidean plane geometry. For example, the sum of the interior angles of any triangle is always greater than 180°.

- https://en.wikipedia.org/wiki/Versor - an algebraic parametrisation of rotations. In classical quaternion theory a versor is a quaternion of norm one (a unit quaternion).

### Convex geometry

- https://en.wikipedia.org/wiki/Convex_set - In Euclidean space, an object is convex if for every pair of points within the object, every point on the straight line segment that joins the pair of points is also within the object. For example, a solid cube is convex, but anything that is hollow or has a dent in it, for example, a crescent shape, is not convex. A convex curve forms the boundary of a convex set. The notion of a convex set can be generalized to other spaces.

- Feeling Your Way Around in High Dimensions - The simplest objects of interest in any dimension, which are also the basis for approximating arbitrary objects, are the convex polytopes and in this column I'll explain how to begin to probe them...

### Trigonometry

- https://en.wikipedia.org/wiki/Trigonometry - studies relationships involving lengths and angles of triangles. The field emerged during the 3rd century BC from applications of geometry to astronomical studies. The 3rd-century astronomers first noted that the lengths of the sides of a right-angle triangle and the angles between those sides have fixed relationships: that is, if at least the length of one side and the value of one angle is known, then all other angles and lengths can be determined algorithmically. These calculations soon came to be defined as the trigonometric functions and today are pervasive in both pure and applied mathematics: fundamental methods of analysis such as the Fourier transform, for example, or the wave equation, use trigonometric functions to understand cyclical phenomena across many applications in fields as diverse as physics, mechanical and electrical engineering, music and acoustics, astronomy, ecology, and biology. Trigonometry is also the foundation of surveying.

- https://en.wikipedia.org/wiki/Sine - a trigonometric function of an angle. The sine of an angle is defined in the context of a right triangle: for the specified angle, it is the ratio of the length of the side that is opposite that angle (that is not the hypotenuse) to the length of the longest side of the triangle (i.e., the hypotenuse).

### Topology

- https://en.wikipedia.org/wiki/Topology - the mathematical study of shapes and topological spaces. It is an area of mathematics concerned with the properties of space that are preserved under continuous deformations including stretching and bending, but not tearing or gluing. This includes such properties as connectedness, continuity and boundary. Topology developed as a field of study out of geometry and set theory, through analysis of such concepts as space, dimension, and transformation. Such ideas go back to Leibniz, who in the 17th century envisioned the geometria situs (Greek-Latin for "geometry of place") and analysis situs (Greek-Latin for "picking apart of place"). The term topology was introduced by Johann Benedict Listing in the 19th century, although it was not until the first decades of the 20th century that the idea of a topological space was developed. By the middle of the 20th century, topology had become a major branch of mathematics.

- https://en.wikipedia.org/wiki/Topos - a type of category that behaves like the category of sheaves of sets on a topological space (or more generally: on a site). Topoi behave much like the category of sets and possess a notion of localization; they are in a sense a generalization of point-set topology. The Grothendieck topoi find applications in algebraic geometry; the more general elementary topoi are used in logic.

- https://en.wikipedia.org/wiki/General_topology - the branch of topology that deals with the basic set-theoretic definitions and constructions used in topology. It is the foundation of most other branches of topology, including differential topology, geometric topology, and algebraic topology. Another name for general topology is
**point-set topology**. The fundamental concepts in point-set topology are continuity, compactness, and connectedness: Continuous functions, intuitively, take nearby points to nearby points; Compact sets are those that can be covered by finitely many sets of arbitrarily small size; Connected sets are sets that cannot be divided into two pieces that are far apart.

- https://en.wikipedia.org/wiki/Algebraic_topology - branch of mathematics that uses tools from abstract algebra to study topological spaces. The basic goal is to find algebraic invariants that classify topological spaces up to homeomorphism, though usually most classify up to homotopy equivalence. Although algebraic topology primarily uses algebra to study topological problems, using topology to solve algebraic problems is sometimes also possible. Algebraic topology, for example, allows for a convenient proof that any subgroup of a free group is again a free group.

- https://en.wikipedia.org/wiki/Differential_topology - the field dealing with differentiable functions on differentiable manifolds. It is closely related to differential geometry and together they make up the geometric theory of differentiable manifolds.

- https://en.wikipedia.org/wiki/Geometric_topology - the study of manifolds and maps between them, particularly embeddings of one manifold into another.

- https://en.wikipedia.org/wiki/Topological_space - a set of points, along with a set of neighbourhoods for each point, that satisfy a set of axioms relating points and neighbourhoods. The definition of a topological space relies only upon set theory and is the most general notion of a mathematical space that allows for the definition of concepts such as continuity, connectedness, and convergence. Other spaces, such as manifolds and metric spaces, are specializations of topological spaces with extra structures or constraints. Being so general, topological spaces are a central unifying notion and appear in virtually every branch of modern mathematics. The branch of mathematics that studies topological spaces in their own right is called point-set topology or general topology.

- https://en.wikipedia.org/wiki/Topological_group - a group G together with a topology on G such that the group's binary operation and the group's inverse function are continuous functions with respect to the topology. A topological group is a mathematical object with both an algebraic structure and a topological structure. Thus, one may perform algebraic operations, because of the group structure, and one may talk about continuous functions, because of the topology. Topological groups, along with continuous group actions, are used to study continuous symmetries, which have many applications, for example in physics.

- https://en.wikipedia.org/wiki/Neighbourhood_(mathematics) - a neighbourhood of a point is a set containing the point where you can move that point some amount without leaving the set.

- https://en.wikipedia.org/wiki/Metric_space - a set for which distances between all members of the set are defined. Those distances, taken together, are called a metric on the set.

The most familiar metric space is 3-dimensional Euclidean space. In fact, a "metric" is the generalization of the Euclidean metric arising from the four long-known properties of the Euclidean distance. The Euclidean metric defines the distance between two points as the length of the straight line segment connecting them. Other metric spaces occur for example in elliptic geometry and hyperbolic geometry, where distance on a sphere measured by angle is a metric, and the hyperboloid model of hyperbolic geometry is used by special relativity as a metric space of velocities.

A metric on a space induces topological properties like open and closed sets, which lead to the study of more abstract topological spaces. In the most general definition of a metric space, the distance between set elements can be negative. Spaces like these are important in the theory of relativity.

- https://en.wikipedia.org/wiki/Manifold - a topological space that resembles Euclidean space near each point

- https://en.wikipedia.org/wiki/Scheme_(mathematics)
- https://en.wikipedia.org/wiki/Glossary_of_scheme_theory

- JTS Topology Suite - an API of spatial predicates and functions for processing geometry. It has the following design goals: JTS conforms to the Simple Features Specification for SQL published by the Open Geospatial Consortium. JTS provides a complete, consistent, robust implementation of fundamental algorithms for processing linear geometry on the 2-dimensional Cartesian plane. JTS is fast enough for production use JTS is written in 100% pure Java.

### Reverse mathematics

## Probability theory

### Statistics

- https://github.com/mavam/stat-cookbook
- https://normaldeviate.wordpress.com/2012/11/17/what-is-bayesianfrequentist-inference
- http://www.greenteapress.com/thinkbayes

- http://www.mcgrayne.com/the_theory_that_would_not_die__how_bayes__rule_cracked_the_enigma_code__hunted_d_107493.htm [69]

## Information theory

## Cellular automaton

## Software

SEe also JS scripts#Maths

- Mathics is a free, general-purpose online computer algebra system featuring Mathematica-compatible syntax and functions. It is backed by highly extensible Python code, relying on SymPy for most mathematical tasks and, optionally, Sage for more advanced stuff. [75]

- http://www.p-value.info/2012/11/free-datascience-books.html
- How to implement an algorithm from a scientific paper

- SageMath is a free open-source mathematics software system licensed under the GPL. It builds on top of many existing open-source packages: NumPy, SciPy, matplotlib, Sympy, Maxima, GAP, FLINT, R and many more. Access their combined power through a common, Python-based language or directly via interfaces or wrappers.

Mission: Creating a viable free open source alternative to Magma, Maple, Mathematica and Matlab.

- http://blog.stephenwolfram.com/2014/08/computational-knowledge-and-the-future-of-pure-mathematics/ [77]

#### to sort

- https://chorasimilarity.wordpress.com/graphic-lambda-calculus/
- http://chorasimilarity.github.io/chemlambda-gui

#### Agda

#### Isabelle

#### Idris

- Idris - a general purpose pure functional programming language with dependent types. Dependent types allow types to be predicated on values, meaning that some aspects of a program’s behaviour can be specified precisely in the type. It is compiled, with eager evaluation. Its features are influenced by Haskell and ML,

#### Albatros

- http://albatross-lang.sourceforge.net/ a programming language which can be verified statically. You write programs in Albatross and prove them to be correct in the same language., What is a correct program? A program is correct if it is consistent with its specification. Specifications in Albatross are assertions which express correctness conditions. Assertions are boolean expressions in predicate logic. A verified Albatross program has as proof for each assertion. The proof is generated by the compiler.m But since assertions are expressed in predicate logic and predicate logic is not decidable for arbitrary expressions the theorem prover in the Albatross compiler cannot prove all valid assertions. Therefore the programmer has to provide the proof steps which cannot be done by the compiler automatically.

#### Coq

## Visualisation

to find those prime vis things again

### Gephi

- Gephi is an interactive visualization and exploration platform for all kinds of networks and complex systems, dynamic and hierarchical graphs.
- https://wiki.gephi.org
- http://en.wikipedia.org/wiki/Gephi

### Fractals

- YouTube: Fractals are not self-similar

- http://en.wikipedia.org/wiki/Julia_set
- http://acko.net/blog/how-to-fold-a-julia-fractal/
- http://sprott.physics.wisc.edu/carlson/dragons.html

- https://en.wikipedia.org/wiki/Mandelbrot_set
- YouTube: The Mandelbrot Set - Numberphile

### Software

- mandelstir - Animating fractional iterations in the Mandelbrot Set and Julia Sets.

- Mandelbulber is an experimental application that helps to make rendering 3D Mandelbrot fractals much more accessible. A few of the supported 3D fractals: Mandelbulb, Mandelbox, BulbBox, JuliaBulb, Menger Sponge, Quaternion, Trigonometric, Hypercomplex, and Iterated Function Systems (IFS). All of these can be combined into infinite variations with the ability to hybridize different formulas together.

- FractalNow - A fast, advanced, multi-platform fractal generator.

- Fraqtive is an open source, multi-platform generator of the Mandelbrot family fractals. It uses very fast algorithms supporting SSE2 and multi-core processors. It generates high quality anti-aliased images and renders 3D scenes using OpenGL. It allows real-time navigation and dynamic generation of the Julia fractal preview.

- Fragmentarium is an open source, cross-platform IDE for exploring pixel based graphics on the GPU. It is inspired by Adobe's Pixel Bender, but uses GLSL, and is created specifically with fractals and generative systems in mind.

### Other

## Informatics

## Nature

## to sort

- http://mathoverflow.net/questions/156263/perfectly-centered-break-of-a-perfectly-aligned-pool-ball-rack/156407#156407 [92]
- https://en.wikipedia.org/wiki/Theory_of_relations

- http://www.wisdomandwonder.com/link/6582/some-thoughts-on-mathematics
- http://news.ycombinator.com/item?id=4839881
- http://www.evanmiller.org/mathematical-hacker.html http://www.evanmiller.org/mathematical-hacker.html]

- https://en.wikipedia.org/wiki/Transformation_(function) - a function f that maps a set X to itself, i.e. f : X → X. In other areas of mathematics, a transformation may simply be any function, regardless of domain and codomain. This wider sense shall not be considered in this article; refer instead to the article on function for that sense.

Examples include linear transformations and affine transformations, rotations, reflections and translations. These can be carried out in Euclidean space, particularly in R2 (two dimensions) and R3 (three dimensions). They are also operations that can be performed using linear algebra, and described explicitly using matrices.

- https://jackschaedler.github.io/circles-sines-signals/
- http://blog.revolutionanalytics.com/2014/01/the-fourier-transform-explained-in-one-sentence.html [94]
- http://www.altdevblogaday.com/2011/05/17/understanding-the-fourier-transform/
- http://betterexplained.com/articles/an-interactive-guide-to-the-fourier-transform/
- http://toxicdump.org/stuff/FourierToy.swf [95]
- http://bl.ocks.org/jinroh/7524988
- https://news.ycombinator.com/item?id=7789767
- http://nautil.us/blog/the-math-trick-behind-mp3s-jpegs-and-homer-simpsons-face
- Fourier Analysis (and guitar jammin') - Sixty Symbols
- Every picture is made of waves - Sixty Symbols
- http://david.li/filtering/ [96]
- http://www.leancrew.com/all-this/2015/01/the-michelson-fourier-analyzer/ [97]
- http://bgrawi.com/Fourier-Visualizations/ [98]