\begin{prooftree}
\AxiomC{$A(a) \rightarrow A(a)$}
\AxiomC{$B \rightarrow B$}
\doubleLine
\RightLabel{[detachment]}
\BinaryInfC{$A(a), (A(a) \supset B) \rightarrow B$}
\RightLabel{[$\forall$L]}
\UnaryInfC{$\forall x A(x), (A(a) \supset B) \rightarrow B$}
\RightLabel{[$\supset$R]}
\UnaryInfC{$(A(a) \supset B) \rightarrow (\forall x A(x) \supset B)$}
\RightLabel{[$\exists$L]}
\UnaryInfC{$\exists x (A(x) \supset B) \rightarrow (\forall x A(x) \supset B)$}
\end{prooftree}
