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Thread: Equivalent Subspaces

  1. #1
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    Equivalent Subspaces

    For each $\displaystyle n\in\mathbb{N}$ give examples of subspaces of $\displaystyle \mathbb{R}^n$, which are homotopy equivalent but not homeomorphic to each other.

    Give reasons for your answer.

    Any help would be great. Thanks
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  2. #2
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    Quote Originally Posted by ejgmath View Post
    For each $\displaystyle n\in\mathbb{N}$ give examples of subspaces of $\displaystyle \mathbb{R}^n$, which are homotopy equivalent but not homeomorphic to each other.

    Give reasons for your answer.

    Any help would be great. Thanks

    One open and and one closed intervals (balls if $\displaystyle n>1$): they're trivially homotopic but not homeomorphic.

    Tonio
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  3. #3
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    Okay, so if I take an open ball $\displaystyle B_r({\bf{x}})$ in $\displaystyle \mathbb{R}^n$ this is clearly not homeomorphic to a point $\displaystyle {\bf{y}}$ in $\displaystyle \mathbb{R}^n$ as any continous map is not bijective.

    So take a map $\displaystyle f:B_r({\bf{x}})\rightarrow {\bf{y}}$ given by $\displaystyle f({\bf{v}})={\bf{y}}$ for $\displaystyle {\bf{v}}\in B_r({\bf{x}})$ and then take another map $\displaystyle g:{\bf{y}}\rightarrow B_r({\bf{x}})$ given by $\displaystyle g({\bf{y}})={\bf{x}}$

    How do I should that $\displaystyle g\circ f$ and $\displaystyle f\circ g$ are homotopic to the respective identities?
    Last edited by ejgmath; Apr 26th 2010 at 07:55 AM.
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