\begin{xy} \xymatrix{ & x^{y'} \otimes y \ar[ld]_-{x^g \otimes y} \ar[rd]^-{x^{y'} \otimes g} \\ x^y \otimes y \ar[rd]_{ {\rm eval}_{x,y}} & & x^{y'} \otimes y' \ar[ld]^{ {\rm eval}_{x,y'}} \\ & x } \end{xy}