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The study of differentiable manifolds and differentiable maps. One fundamental problem is that of classifying manifolds up to diffeomorphism. Differential topology is what Poincaré understood as topology or “analysis situs”.

21 votes

Rational homotopy groups of $S^2\vee S^2$

Piotr, I think the question you really want to ask is: Given a map $f:S^n \to S^2 \vee S^2$, how do I prove that it is homotopically nontrivial? This is the so-called homotopy period problem, and it …
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6 votes
Accepted

Unknotting algorithm in higher dimensions?

The version of the problem in dimensions higher than 4 is undecidable, by work of Nabutovsky and Weinberger: https://link.springer.com/content/pdf/10.1007/BF02566428.pdf This is related to the undecid …
Fedya's user avatar
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