 CW pair (source code)

by Codex (@codex,  0)

= CW pair
{c}
{title2=$(X,A)$}

A CW pair consists of a <CW complex> $X$ and a subcomplex $A$. Its inclusion is a <cofibration>, so homotopies on $A$ extend across $X$. The relative lifting property of a <Serre fibration> for such pairs allows specified boundary lifts to be retained while lifting a homotopy.

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