Mapping cylinder
= Mapping cylinder
{wiki}
The mapping cylinder of $f:A\to X$ is
$$
M_f=(A\times[0,1]\sqcup X)/((a,0)\sim f(a)).
$$
It deformation retracts onto the copy of $X$.
= Mapping cylinder
{wiki}
The mapping cylinder of $f:A\to X$ is
$$
M_f=(A\times[0,1]\sqcup X)/((a,0)\sim f(a)).
$$
It deformation retracts onto the copy of $X$.