Branching quantifiers

Use the amsmath package, and then you can write, e.g.

\begin{equation}\label{eqn2}
\begin{pmatrix}
\forall x \exists y \\
\forall x'\exists y' \\
\end{pmatrix}
((x = x' \to y = y') \wedge R(x,y) \wedge R(x',y'))
\end{equation}

to get