The Szczarba map and the cubical cobar construction

We consider a twisting function from a 1-reduced simplicial set $X$ to a simplicial group $G$. We prove in detail that the associated Szczarba operators induce a simplicial map from the triangulation of the cubical cobar construction of $X$ to $G$. This confirms a result due to Minichiello-Rivera-Zeinalian and gives, as pointed out by these authors, a conceptual proof of the fact that the dga map $\mathrm{\Omega }C(X)\to C(G)$ induced by Szczarba’s twisting cochain is comultiplicative.