|
|
$$\begin{array}{rlrl}
1&{_{\:\!\mathbf|}}\!\underline{\,~\neg \exists xPx~}\\[-5pt]
2&\big|~{_{\:\!\mathbf|}}\!\underline{\,~Pa~}\\[-5pt]
3&\big|~\big|~\exists xPx&\rm{{\exists}I}&\rm{2}\\[-5pt]
4&\big|~\big|~\bot&\rm{{\neg}E}&\rm{1,3}\\[-5pt]
5&\big|~\neg Pa&\rm{{\neg}I}&\rm{2{-}4}\\[-5pt]
6&\big|~\forall x\neg Px&\rm{{\forall}I}&\rm{5}\\[-5pt]
\end{array}$$
|