# Kerodon

$\Newextarrow{\xRightarrow}{5,5}{0x21D2}$ $\newcommand\empty{}$

Remark 2.5.7.16. Corollary 2.5.7.15 is essentially due to Eilenberg and Zilber. More precisely, in [MR52767], Eilenberg and Zilber proved that there exists a collection of quasi-isomorphisms $G_{S,T}: \mathrm{N}_{\ast }(S; \operatorname{\mathbf{Z}}) \boxtimes \mathrm{N}_{\ast }(T; \operatorname{\mathbf{Z}}) \rightarrow \mathrm{N}_{\ast }(S \times T; \operatorname{\mathbf{Z}})$ depending functorially on the simplicial sets $S_{\bullet }$ and $T_{\bullet }$. The proof given in [MR52767] uses the method of acyclic models and does not provide a concrete description of the maps $G_{S,T}$. However, it is not difficult to see that such a collection of chain maps $\{ G_{S,T} \}$ must coincide up to sign with the Eilenberg-Zilber homomorphisms of Example 2.5.7.12 (see Exercise 2.5.7.18 below).