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\setlength\subproofhorizspace{1.1em}
\begin{logicproof}{1}
\exists x \forall y \; (P(y) \imp Q(x)) & prem.\\
\forall s \; \lnot Q(s) \land R(s) & prem.\\
\begin{subproof}
\llap{$t\enspace \;$} \forall y \; (P(y) \imp Q(t)) & ass.\\
P(t) \imp Q(t) & $\forall \mathrm{e}$ 3\\
\lnot Q(t) \land R(s) & $\forall \mathrm{e}$ 2\\
\lnot Q(t) & $\land \mathrm{e}_1$ 5\\
\lnot P(t) & MT 4,6\\
\exists x \; \lnot P(t) & $\exists \mathrm{i}$ 7\\
\lnot R(s) & $\land \mathrm{e}_2$ 5\\
R(s) \imp \exists x \; \lnot P(t) & $\exists \mathrm{i}$ 7\\
\end{subproof}
R(s) \imp \exists x \; \lnot P(t) & $\exists \mathrm{e}$ 3-10
\end{logicproof}