===== Retraction =====
==== Set ====
| $X,S$ |

| $S\subseteq X$ |

^ $ \{\rho\} $ ^

| $ \rho:X\to S $ |

^ $ \rho_{|S}=\text{id}_S $ ^

==== Ramifications ====
==== Reference ====
Wikipedia: [[http://en.wikipedia.org/wiki/Deformation_retract|Deformation retract]]
==== Parents ====
=== Related ===
[[Identity relation]]