(P∨Q)∧P⇔P

証明

https://scrapbox.io/files/68aebd5d76fb6820ac24e6cc.svg

https://scrapbox.io/files/68aebdc4d36a31a7932d1bd5.svg

code:l2r.tikz(tex)

\usepackage{fitch}

\usepackage{amsmath}

\begin{document}

$\Large\begin{nd}

\hypo {l} {(P\lor Q)\land P}

\have {r} {P} \ae{l}

\end{nd}$

\end{document}

code:r2l.tikz(tex)

\usepackage{fitch}

\usepackage{amsmath}

\begin{document}

$\Large\begin{nd}

\hypo {r} {P}

\have {pq} {P\lor Q} \oi{r}

\have {l} {(P\lor Q)\land P} \ai{r,pq}

\end{nd}$

\end{document}