Employing the notation introduced in Notation 4.5.1.1.6, we have
\begin{align*} x_{0}\wedge y_{0} & = x\wedge y_{0},\\ & = x_{0}\wedge y\end{align*}
for each $x\in X$ and each $y\in Y$, and
\begin{align*} x\wedge y_{0} & = x'\wedge y_{0},\\ x_{0}\wedge y & = x_{0}\wedge y’\end{align*}
for each $x,x'\in X$ and each $y,y'\in Y$.
