exactness theorem
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Mitchell's embedding theorem — Mitchell s embedding theorem, also known as the Freyd–Mitchell theorem, is a result stating that every abelian category admits a full and exact embedding into the category of R modules. This allows one to use element wise diagram chasing proofs… … Wikipedia
Mayer–Vietoris sequence — In mathematics, particularly algebraic topology and homology theory, the Mayer–Vietoris sequence is an algebraic tool to help compute algebraic invariants of topological spaces, known as their homology and cohomology groups. The result is due to… … Wikipedia
Splitting lemma — In mathematics, and more specifically in homological algebra, the splitting lemma states that in any abelian category, the following statements for short exact sequence are equivalent. Given a short exact sequence with maps q and r: :0 ightarrow… … Wikipedia
Spin structure — In differential geometry, a spin structure on an orientable Riemannian manifold allows one to define associated spinor bundles, giving rise to the notion of a spinor in differential geometry. Spin structures have wide applications to mathematical … Wikipedia
Projective module — In mathematics, particularly in abstract algebra and homological algebra, the concept of projective module over a ring R is a more flexible generalisation of the idea of a free module (that is, a module with basis vectors). Various equivalent… … Wikipedia
Five lemma — In mathematics, especially homological algebra and other applications of Abelian category theory, the five lemma is an important and widely used lemma about commutative diagrams.The five lemma is valid not only for abelian categories but also… … Wikipedia
Algebraic number field — In mathematics, an algebraic number field (or simply number field) F is a finite (and hence algebraic) field extension of the field of rational numbers Q. Thus F is a field that contains Q and has finite dimension when considered as a vector… … Wikipedia
Étale cohomology — In mathematics, the étale cohomology groups of an algebraic variety or scheme are algebraic analogues of the usual cohomology groups with finite coefficients of a topological space, introduced by Grothendieck in order to prove the Weil… … Wikipedia
Pappus of Alexandria — (Greek polytonic|Πάππος ὁ Ἀλεξανδρεύς) (c. 290 ndash; c. 350) was one of the last great Greek mathematicians of antiquity, known for his Synagoge or Collection (c. 340), and for Pappus s Theorem in projective geometry. Nothing is known of his… … Wikipedia
Snake lemma — The snake lemma is a tool used in mathematics, particularly homological algebra, to construct long exact sequences. The snake lemma is valid in every abelian category and is a crucial tool in homological algebra and its applications, for instance … Wikipedia
Hume's principle — Hume s Principle, or HP the terms were coined by George Boolos mdash;says that the number of F s is equal to the number of G s if there is a one to one correspondence (a bijection) between the F s and the G s. HP can be stated formally in systems … Wikipedia
