Can somebody come up with an example where $X \subset Y$, the inclusion gives a homotopy equivalence between $X$ and $Y$, but there is no deformation retraction from $Y$ onto $X$?
2026-05-14 17:07:20.1778778440
Homotopy equivalent but not deformation retraction
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There are known examples of spaces which are contractible but do not deformation retract onto any point in them. So you can take $Y$ to be such a space and $X$ to be any point in it.