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Homotopy theory, homological algebra, algebraic treatments of manifolds.

3 votes
Accepted

Why does $p_*p^! A$ deserve to be called homology with coefficients in $A$?

One nice geometric way to view homology is a measurement of your space $X$ given by probing $X$ with other, nicer spaces, for instance, singular homology probes with simplices. One good reason to call …
Chris H's user avatar
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14 votes
1 answer
700 views

Is there a concrete description of the nontorsion elements in the homotopy groups of spheres?

By Serre's theorem, we know the only nontorsion parts of the homotopy groups of spheres occur as $\pi_n(S^n)$ and $\pi_{4n-1}(S^{2n})$. The first of these are trivial to describe, but the second have …