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# homotopy extension property

Let $X$ be a topological space and $A$ a subspace of $X$. Suppose there is a continuous map $f:X\to Y$ and a homotopy of maps $F:A\times I\to Y$. The inclusion map $i:A\to X$ is said to have the *homotopy extension property* if there exists a continuous map $F^{{{}^{{\prime}}}}$ such that the following diagram commutes:

$\SelectTips{eu}{}\xymatrix{&A\ar[d]^{{i}}\ar[r]^{{i_{{0}}}}&A\times I\ar[d]^{{% F}}\ar@/^{1}.5pc/[dd]^{{i\times id_{{I}}}}\\ &X\ar[r]^{{f}}\ar[dr]^{{i_{{0}}}}&Y\\ &&X\times I\ar[u]_{{F^{{{}^{{\prime}}}}}}}$ |

Here, $i_{0}=(x,0)$ for all $x\in X$.

Related:

Cofibration, HomotopyLiftingProperty

Type of Math Object:

Definition

Major Section:

Reference

## Mathematics Subject Classification

55P05*no label found*

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new question: A problem about Euler's totient function by mbhatia

new problem: Problem: Show that phi(a^n-1), (where phi is the Euler totient function), is divisible by n for any natural number n and any natural number a >1. by mbhatia

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new image: plot W(t) = P(waiting time <= t) by robert_dodier