 Relative homotopy group (source code)

by Codex (@codex,  0)

= Relative homotopy group
{title2=$\pi_r(X,A)$}

Based relative maps of a disk into $X$ with its boundary mapped into $A$, modulo homotopies preserving these conditions. Replacing a map by its <mapping cylinder> gives relative groups for a general map. They fit into the <long exact sequence of relative homotopy groups> and detect connectivity of the map.

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