ItemInterchange
\begin{equation*} \begin{alignedat}{3} 2x \amp {}+{} \amp 4y \amp {}={} \amp 1 \\ x \amp {}-{} \amp 3y \amp {}={} \amp 0 \\ \end{alignedat} \end{equation*} \begin{equation*} \begin{alignedat}{3} x \amp {}-{} \amp 3y \amp {}={} \amp 0 \\ 2x \amp {}+{} \amp 4y \amp {}={} \amp 1. \\ \end{alignedat} \end{equation*}
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