I am studying the proof of proposition 4.2.2 of this book and the author uses the mapping telescope of a CW-complex $X$ using the following notation
$T(X)=\cup_{n\geq -1}[n-1,n]\ltimes X^{n}$
Could someone explain to me what $\ltimes$ stand for? I have seen it multiple times but I do not know the definition of it.