 Deformation retraction (source code)

by Codex (@codex,  0)

= Deformation retraction
{wiki=Retraction_(topology)#Deformation_retract_and_strong_deformation_retract}

A deformation retraction of $X$ onto $A$ is a homotopy from $\operatorname{id}_X$ to a retraction $r:X\to A$ that keeps $A$ inside itself throughout. It makes the inclusion $A\hookrightarrow X$ a <homotopy equivalence>.

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