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A manifold is a topological space that locally resembles Euclidean space near each point. More precisely, each point of an n-dimensional manifold has a neighbourhood that is homeomorphic to the Euclidean space of dimension n.

21 votes
1 answer
1k views

isotopy inverse embeddings vs. diffeomorphisms

I would like to find an example, if one exists, of manifolds $M$ and $N$ with embeddings $f:M\to N$ and $g:N\to M$ such that $f\circ g$ and $g\circ f$ are both isotopic (i.e. homotopic through embeddings … You may assume that the manifolds have no boundary, but I would also be interested in compact examples. …
Ricardo Andrade's user avatar
18 votes
Accepted

Cancellation law for $M^n\times \mathbb R= N^n\times \mathbb R$.

closed, smooth manifolds of dimension greater than 3, then $M\times\RR$ is diffeomorphic to $N\times\RR$. … The article "Contact manifolds with symplectomorphic symplectizations" states the result for smooth manifolds as corollary 2.5. [The proof described there applies also to topological manifolds.] …
Ricardo Andrade's user avatar
15 votes
Accepted

homotopy type of embeddings versus diffeomorphisms

Personal comment: It seems the discussion in this question finally led me to understand how to modify Agol's argument to answer the present question. In fact, my motivation when asking that question a …
Ricardo Andrade's user avatar
17 votes
2 answers
2k views

homotopy type of embeddings versus diffeomorphisms

Previously, I asked a question on mathoverflow comparing smooth embeddings and diffeomorphisms, which received a very interesting and somewhat unexpected answer by Agol. I now ask a further question a …
Ricardo Andrade's user avatar
10 votes
Accepted

Reference Request: Compact manifolds with boundary have the homotopy type of a CW-complex

However, it can be deduced from the following fact: topological manifolds (paracompact and Hausdorff) are absolute neighbourhood retracts, and thus have the homotopy type of CW-complexes. … For the specific case of compact manifolds, an elementary proof is given in the appendix of Hatcher's book Algebraic topology (see corollary A.12 there). We can now prove the result you state. …
Ricardo Andrade's user avatar
11 votes

Distinct manifolds with the same configuration spaces?

I will present an example involving only (non-compact) manifolds without boundary. As far as I know, the analogous problem for closed manifolds is wide open. … A few consequences of this are: An embedding $V \to W$ between contractible $n$-manifolds without boundary induces a homotopy equivalence on all ordered and unordered configuration spaces. …
Ricardo Andrade's user avatar