$b = $ I press the button. \\
$w = $ The window is open. \\

\bigskip

$b \implies w, \lnot w \entails \lnot b$
\begin{logicproof}{2}
    b \implies w & \prem \\
    \lnot w & \prem \\
    \begin{subproof}
        b & \assum \\
        w & $\impe 1,3$ \\
        \false & $\nege 2,4$
    \end{subproof}
    \lnot b & $\negi 3-5$
\end{logicproof}