Consider $D = C$: Thus $C \in \py, L \in \py$.
By Tip Own Contents, $L \haspatch \p$ so $L \neq X$,
therefore we must have $L=Y$, $R=X$.
Consider $D = C$: Thus $C \in \py, L \in \py$.
By Tip Own Contents, $L \haspatch \p$ so $L \neq X$,
therefore we must have $L=Y$, $R=X$.