It is possibly relevant toIt is possibly relevant to note that, by definition, $|p|$ is a cellular map. If $e$ is a cell of $|E|$ with its natural CW structure, so too is $|p|(e)$ a cell of $|X|$. Conversely, $|p|^{-1}(e)$ is a disjoint union of cells in $|E|$ for every cell $e$ of $|X|$. I think this could be useful. As a note that,to myself (inspired by definitionMaxime’s answer), $|p|$ is a cellular map. If $e$this is a cellonly true by invariance of domain for homeomorphisms $|E|$ with its natural CW structure$p$, so too is $|p|(e)$since we can have in general a cellmapping of a nondegenerate $|X|$. Conversely,$n$-simplex $|p|^{-1}(e)$ is a disjoint union of cells(corresponding to an $n$-cell in the CW structure) to a degenerate one $|E|$ for every(not corresponding to any particular cell $e$ of $|X|$. I think this could be useful) which breaks the argument.