+\subsection{Merge Contributors for $\pcy$}
+
+Merge $\pcn$ into $\grefc$. That is, merge with
+$L = \grefc, R = \greffa{\pcn}, M = \baseof{\grefc}$.
+to construct $\grefu$.
+
+Merge conditions: Ingredients satisfied by construction.
+Tip Merge satisfied by construction. Merge Acyclic follows
+from Perfect Contents and $\hasdep$ being acyclic.
+
+Removal Merge Ends: For $\p = \pc$, $M \nothaspatch \p$.
+For $p \neq \pc$, by Tip Contents,
+$M \haspatch \p \equiv L \haspatch \p$, so we need only
+worry about $X = R, Y = L$; ie $L \haspatch \p$,
+$M = \baseof{L} \haspatch \p$.
+By Tip Contents for $L$, $D \le L \equiv D \le M$. $\qed$
+
+OK
+UP TO HERE