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28 votes
4 answers
4k views

Classifying Space of a Group Extension

Consider a short exact sequence of Abelian groups -- I'm happy to assume they're finite as a toy example: $$ 0 \to H \to G \to G/H \to 0\ . $$ I want to understand the classifying space of $G$. Since ...
Aaron Bergman's user avatar
22 votes
6 answers
2k views

Is any interesting question about a group G decidable from a presentation of G?

We say that a group G is in the class Fq if there is a CW-complex which is a BG (that is, which has fundamental group G and contractible universal cover) and which has finite q-skeleton. Thus F0 ...
Chad Groft's user avatar
  • 1,219
7 votes
2 answers
860 views

mapping space between classifying spaces

I wanted to ask a summary of known results and references about the homotopy type of the mapping space $\mathrm{Map}(BG,BK)$ (and specially the connected components) between the classifying spaces ...
Ilias A.'s user avatar
  • 1,974