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Smooth manifolds and smooth functions between them. For manifolds with additional structure, see more specific tags, such as [riemannian-geometry]. For more topological aspects, see [differential-topology].

14 votes

Is each closed convex set a manifold with corners?

Let $C \subset S^1 \subset \mathbb{R}^2$ be a Cantor set. Let $H_C$ be its convex hull, the smallest closed subset of $\mathbb{R}^2$ containing $C$. Then $H_C$ is not a manifold with corners. Its boun …
Lee Mosher's user avatar
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21 votes
1 answer
2k views

Manifolds with two coordinate charts

What is an early reference for the fact that if a compact, connected $n$-manifold $M$ is covered by two open sets homeomorphic to $\mathbb{R}^n$ then $M$ is homeomorphic to $S^n$? And is it true that …
Lee Mosher's user avatar
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3 votes
Accepted

Is the following 3-manifold irreducible?

Yes, $Y$ is still irreducible, and this holds by a simple connectivity argument. Suppose that $\Sigma \subset Y \subset X$ is a smoothly embedded 2-sphere. Since $X$ is irreducible, $\Sigma$ bounds …
Lee Mosher's user avatar
  • 15.4k
5 votes

How to get convinced that there are a lot of 3-manifolds?

Read Chapter 4 of Thurston's notes http://library.msri.org/books/gt3m/. He produces infinitely many closed hyperbolic 3-manifold of different volumes, and hence non-homeomorphic, just by doing Dehn su …
Lee Mosher's user avatar
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3 votes

Markov Partitions for toral automorphisms

To address your second question, there is a simple construction of a Markov partition which inputs not "any topological partition" but which simply inputs the matrix $M \in SL_2(Z)$ that represents $T …
Lee Mosher's user avatar
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