# retract

Let $X$ be a topological space and $Y$ a subspace of $X$. If there exists a continuous map $r:X\to Y$ such that $r(y)=y$ for all $y\in Y$, then we say $Y$ is a retract of $X$ and $r$ is a retraction.

Title retract Retract 2013-03-22 12:16:06 2013-03-22 12:16:06 rspuzio (6075) rspuzio (6075) 6 rspuzio (6075) Definition msc 54C15 DeformationRetraction PeriodOfMapping retraction