Hatcher-Algebraic-Topology · Problem 4.H.2

Homotopy Theory

Mathematics — Graph Theory · eckmann-hilton-duality

Problem

Consider a pushout diagram as at the right, where

B \sqcup_f X

B

with

X

attached along

A

via

f

. Show that if

A \hookrightarrow X

is a cofibration, so is

B \hookrightarrow B \sqcup_f X