# Hatcher 0.28

Hatcher, Algebraic Topology, Chapter 0

28. Show that if $(X_1,A)$ satisfies the homotopy extension property, then so does every pair $(X_0\sqcup_f X_1,X_0)$ obtained by attaching $X_1$ to a space $X_0$ via a map $f:A\to X_0$.

Proof.

$\square$