Talk:Extension problem
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I think that the distinction between K being a subgroup of G or only being isomorphic to one is not important, because there is a specific isomorphism between them. This language doesn't really generalize anything, it just makes it a bit more confusing. Gregory Muller 13:58, 11 September 2006 (UTC)
[edit] Merge with Group Extension
I'm not sure there are enough interesting things to say about group extensions other than their classification to merit its own entry. Gregory Muller 13:58, 11 September 2006 (UTC)
- Well, there are entire articles on group cohomology and the ext functor, so it would seem there's a lot to be said ... linas 20:33, 11 March 2007 (UTC)
[edit] Mistake
The claim that Ext1(H,K) classifies central extensions of H by K is wrong. Ext1 classifies only abelian extensions. Central extensions are classified by group cohomology, namely H2(H,K), which is a gadget that makes sense after we've specified an action of H on K. So, someone should fix this. It may have to be me. John Baez 18:32, 26 January 2007 (UTC)
- We'd prefer it was you ... linas 20:35, 11 March 2007 (UTC)
