** Well-ordering theorem: Every set can be well-ordered.

** Tarski's theorem: For every infinite set A, there is a bijective map between the sets A and A × A.

** Zorn's lemma: Every non-empty partially ordered set in which every chain ( i. e. totally ordered subset ) has an upper bound contains at least one maximal element.

** Hausdorff maximal principle: In any partially ordered set, every totally ordered subset is contained in a maximal totally ordered subset.

** Antichain principle: Every partially ordered set has a maximal antichain.

** For every non-empty set S there is a binary operation defined on S that makes it a group.

** If S is a set of sentences of first-order logic and B is a consistent subset of S, then B is included in a set that is maximal among consistent subsets of S. The special case where S is the set of all first-order sentences in a given signature is weaker, equivalent to the Boolean prime ideal theorem ; see the section " Weaker forms " below.

** If the set A is infinite, then there exists an injection from the natural numbers N to A ( see Dedekind infinite ).

** Gödel's completeness theorem for first-order logic: every consistent set of first-order sentences has a completion.

** In particular, the cofinality of any nonzero finite ordinal, or indeed any finite directed set, is 1, since such sets have a greatest element.

** In particular, let A be a set of size n, and consider the set of subsets of A containing no more than m elements.

** Mine Exploder T11: Six forward firing mortars to set off mines.

** " Has the same absolute value " on the set of real numbers

** " Has the same cosine " on the set of all angles.

** Filter ( mathematics ), a special subset of a partially ordered set

** The set of infinite strings is the inverse limit of the set of finite strings, and is thus endowed with the limit topology.

** Written communication ( writing ) – representation of language in a textual medium through the use of a set of signs or symbols ( known as a writing system ).

** Mouthpiece ( scuba ), a component of a scuba diving or industrial breathing set

** Metrics ( networking ), set of properties of a communication path

** Also an older term for the empty set

** 4 8 × 8 single-color user-defined sprites ; each sprite's color may be set independently

** In order theory, see order automorphism.

** Microevolution: species — speciation — adaptation — selection — natural selection — directional selection — sexual selection — genetic drift — sexual reproduction — asexual reproduction — colony — allele frequency — neutral theory of molecular evolution — population genetics — Hardy-Weinberg principle

** Quantum chromodynamics, a theory of the strong interaction ( color force )

** Dual ( category theory ), a formalization of mathematical duality

** LTI system theory

** electron theory of metals

** Backward induction in game theory and economics

** for his profound contributions to three major areas of operations research and management science: inventory theory, dynamic programming and lattice programming.

** in recognition of his fundamental contributions to game theory and related areas

** for his contributions to queueing theory, applied probability and stochastic modelling

** Limit ( category theory )

** Most forms of cognitivism hold that some such propositions are true, as opposed to error theory, which asserts that all are erroneous.

** Error theory, another form of moral anti-realism, holds that although ethical claims do express propositions, all such propositions are false.

** In topos theory, the ( codomain of the ) subobject classifier of an elementary topos.

** In group theory, the omega and agemo subgroups of a p-group, Ω ( G ) and ℧( G )

** In number theory, Ω ( n ) is the number of prime divisors of n.

** In relational database theory to represent NULL, a missing or inapplicable value.

** In number theory, ω ( n ) is the number of distinct prime divisors of n.

** In number theory, an arithmetic function

** the ultraproduct, in model theory.

** General relativity, Albert Einstein's theory of gravitation

** Special relativity, a theory formulated by Albert Einstein, Henri Poincaré, and Hendrik Lorentz

** Constructionism ( learning theory )

** Coherence theory of truth