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\newcommand{\missingcitation}{\rule{5cm}{0.15mm}}
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\begin{document}
%\header

\begin{question}{0. Boolean \missingcitation}
    \textbf{Note:} Download this problem from the website \texttt{cs.uw.edu/390z} and do it in \LaTeX.

    We wish to prove that the following is true for all values of the boolean variables $x$ and $m$:
    \[ m' + \big(x\cdot m + x' \cdot m\big) \]
    The following chain of equivalences does this, but it is missing citations for which rules are used. Fill in the blanks with names of the logic equivalences used at each step.
    \begin{align*}
      m' + \big(x\cdot m + x' \cdot m\big)
        &\equiv m' + \big(m \cdot x + x' \cdot m\big) & \missingcitation \\
        &\equiv m' + \big(m \cdot x + m \cdot x'\big) & \missingcitation \\
        &\equiv m' + m \cdot (x+ x') & \missingcitation \\
        &\equiv m' + m \cdot 1 & \missingcitation \\
        &\equiv m' + m & \missingcitation \\
        &\equiv m + m' & \missingcitation \\
        &\equiv 1 & \missingcitation \\
    \end{align*}
\end{question}
\end{document}
