\(\begin{aligned} & \textcolor{colorprop}{\text{letter 2}} \\ \textcolor{colordef}{\text{letter 1}} \end{aligned} \) | \(\textcolor{colorprop}{N}\) | \(\textcolor{colorprop}{O}\) | \(\textcolor{colorprop}{D}\) | \(\textcolor{colorprop}{E}\) |
\(\textcolor{colordef}{N}\) | X | ? | \(\textcolor{colordef}{N}\textcolor{colorprop}{D}\) | \(\textcolor{colordef}{N}\textcolor{colorprop}{E}\) |
\(\textcolor{colordef}{O}\) | \(\textcolor{colordef}{O}\textcolor{colorprop}{N}\) | X | \(\textcolor{colordef}{O}\textcolor{colorprop}{D}\) | \(\textcolor{colordef}{O}\textcolor{colorprop}{E}\) |
\(\textcolor{colordef}{D}\) | \(\textcolor{colordef}{D}\textcolor{colorprop}{N}\) | \(\textcolor{colordef}{D}\textcolor{colorprop}{O}\) | X | \(\textcolor{colordef}{D}\textcolor{colorprop}{E}\) |
\(\textcolor{colordef}{E}\) | \(\textcolor{colordef}{E}\textcolor{colorprop}{N}\) | \(\textcolor{colordef}{E}\textcolor{colorprop}{O}\) | \(\textcolor{colordef}{E}\textcolor{colorprop}{D}\) | X |