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Homotopy theory, homological algebra, algebraic treatments of manifolds.

35 votes
3 answers
1k views

Incorrect information in an old article about the Kervaire invariant

In the Soviet times there was a famous Encyclopedia of Mathematics. I think it is still familiar to every Russian mathematician maybe except very young ones, and yours truly is in possession …
18 votes
2 answers
1k views

What is the generator of $\pi_9(S^2)$?

This is more or less the same question as [ What is the generator of $\pi_9(S^3)$? ], except what I would like to know is if it is possible to describe this map in a way not only topologists can mak …
17 votes
Accepted

Does the Gauss-Bonnet theorem apply to non-orientable surfaces?

The answer is already given in the comments (by Ryan Budney and Mizar). But I think it makes sense to clear this confusing point. The classical Gauss-Bonnet formula is [e.g. https://en.wikipedia.or …
Alex Gavrilov's user avatar
4 votes
0 answers
88 views

On decidability of a homeomorphism with a prescribed pushforward

This is a refinement of my older question A homeomorphism with a prescribed action on the fundamental group - decidable or not? The problem under considreation is the following. Let $M,N$ be two clo …
9 votes
1 answer
281 views

A homeomorphism with a prescribed action on the fundamental group - decidable or not?

I am curious if the following topological problem is decidable. Let $M,N$ be two closed manifolds. Given a group isomorphism $p: \pi_1(M)\to \pi_1(N)$, is there a homeomorphism $\phi: M\to N$ such …
3 votes
0 answers
234 views

Homotopy type of a locally contractible compact

Does a locally contractible compact space have the homotopy type of a finite CW complex? (I think it probably does, but I need a reference anyway.) EDIT: My intuition was wrong [to see why, read C.T …