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A branch of algebraic topology concerning the study of cocycles and coboundaries. It is in some sense a dual theory to homology theory. This tag can be further specialized by using it in conjunction with the tags group-cohomology, etale-cohomology, sheaf-cohomology, galois-cohomology, lie-algebra-cohomology, motivic-cohomology, equivariant-cohomology, ...

8 votes
1 answer
325 views

Fiber product of spaces and cohomology

I am interested in sufficient conditions on the map $Y \to X$ that ensure that the cohomology of $W$ is the tensor product of the cohomologies of $Y$ and $Z$, $$H^*(W, R) = H^*(Y, R) \otimes_{H^*(X, R …
4 votes

Take contraction wrt a vector field twice and define kernel mod image. Does that give anythi...

I believe that the answer is something in between "not really" and "kind of" and was indicated by Qiaochu Yan. In Wittens famous paper "Morse Theory and Supersymmetry", he considers operators of the …
Matthias Ludewig's user avatar
1 vote
0 answers
400 views

Functors with Mayer-Vietoris Sequences

Let $F$ be a contravariant functor from some category of spaces (e.g. smooth manifolds or (compact?) topological Hausdorff spaces), to Abelian groups. Assume that for any open sets $U, V \subseteq X$ …