Homotopy theory | Homological algebra

Topological half-exact functor

In mathematics, a topological half-exact functor F is a functor from a fixed topological category (for example CW complexes or pointed spaces) to an abelian category (most frequently in applications, category of abelian groups or category of modules over a fixed ring) that has a following property: for each sequence of spaces, of the form: X → Y → C(f) where C(f) denotes a mapping cone, the sequence: F(X) → F(Y) → F(C(f)) is exact. If F is a contravariant functor, it is half-exact if for each sequence of spaces as above,the sequence F(C(f)) → F(Y) → F(X) is exact. Homology is an example of a half-exact functor, andcohomology (and generalized cohomology theories) are examples of contravariant half-exact functors.If B is any fibrant topological space, the (representable) functor F(X)=[X,B] is half-exact. (Wikipedia).

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Related pages

Functor | Cohomology | Module (mathematics) | Mapping cone (topology) | Homology (mathematics) | Mathematics | Pointed space | Category (mathematics)