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\begin{center}
\begin{minipage}{0.2\textwidth}
\begin{prooftree}
\AxiomC{$ \varphi$}
\RightLabel{$ \ori1$}
\UnaryInfC{$ \varphi \lor \psi$}
\end{prooftree}
\end{minipage}
\begin{minipage}{0.2\textwidth}
\begin{prooftree}
\AxiomC{$ \varphi$}
\RightLabel{$ \ori2$}
\UnaryInfC{$ \psi \lor \varphi$}
\end{prooftree}
\end{minipage}
\end{center}
If we know that $\varphi$ holds, we can derive that $\varphi \lor \psi$ holds and that
$\psi \lor \varphi$ holds. This is true for any $\psi$.