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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, ...

15 votes

Can anyone give me a good example of two interestingly different ordinary cohomology theories?

The examples mentioned so far, made the point that Cech cohomology differs from singular cohomology in many examples which are, to the eyes of most topologists, quite pathological. … I want to concentrate on an example of an ordinary homology theory, which is probably much less well known than Cech cohomology, but quite interesting in geometric contexts: stratifold homology (see Kreck's …
Lennart Meier's user avatar
3 votes
2 answers
957 views

Group Cohomology of Symmetric Powers

While for the tensor algebra instead, one could compute its group cohomology via a Künneth theorem [edit: as Thorsten Ekedahl pointed out, this computes only the cohomology of $G\times G$], I have not … So my question is: Is there a general procedure for computing the cohomology groups $H^i(G; Sym(V))$ (with $H^i(G; V)$ as input)? …
Lennart Meier's user avatar
18 votes

de Rham cohomology and flat vector bundles

To a local system one can associate (singular) cohomology groups with local coefficients. … I guess, these cohomology groups with local coefficients should be isomorphic to your ''vector bundle deRham cohomology'', though I know no reference at the moment. …
Lennart Meier's user avatar
6 votes

What is known about K-theory and K-homology groups of (free) loop spaces?

I take the liberty to reference to a paper of mine (which is hopefully no bad style): Spectral Sequences in String Topology. Here, the K-homology of the free loop spaces of spheres and complex project …
Lennart Meier's user avatar
13 votes
Accepted

generalized universal coefficient sequence

an $A_\infty$-ring spectrum (e.g. if $E =ko, ku, KO, KU, TMF, MO, MSO, MSpin \dots$) [EKMM, IV.4] $E$ is even and Landweber exact (e.g. if $E = MU, E(n), E_n, \dots$) [Adams' lectures on generalized cohomology … to Ext^1_{\mathbb{Z}}(E_{k-1}X, \mathbb{Z}) \to (IE)^kX \to Hom_{\mathbb{Z}}(E_kX, \mathbb{Z}) \to 0.$$ That means that there exists always a short exact sequence computing from $E$-homology the $IE$-cohomology
Lennart Meier's user avatar
4 votes

Easier ways to compute homology/cohomology by adding extra structure

Given a Morse function on a Riemannian smooth manifold, you obtain (under mild conditions) a chain complex computing its homology, the Morse complex. Its generators are the critical points and differe …
Lennart Meier's user avatar
4 votes

Occurrences of (co)homology in other disciplines and/or nature

There are some applications of topology/cohomology to combinatorics and combinatoric geometry. … There are many other results in convex geometry/polytope theory which use topological methods and, in particular, cohomology. …
5 votes

A list of machineries for computing cohomology

1) If you want to compute the rational or real cohomology of something, you can try to use rational homotopy theory. … space. 2) If you can show that your space is a $BG$, its cohomology equals the group cohomology of $G$ which is computable in some cases. …