and calculate $\pendsof{C}{\pn}$. So we will consider some
putative ancestor $A \in \pn$ and see whether $A \le C$.
-$A \le C \equiv A \le L \lor A \le R \lor A = C$.
+By Exact Ancestors for C, $A \le C \equiv A \le L \lor A \le R \lor A = C$.
But $C \in py$ and $A \in \pn$ so $A \neq C$.
-Thus $fixme this is not really the right thing A \le L \lor A \le R$.
+Thus $A \le C \equiv A \le L \lor A \le R$.
By Unique Base of L and Transitive Ancestors,
$A \le L \equiv A \le \baseof{L}$.
UP TO HERE
-By Tip Merge, $A \le $
+By Tip Merge condition on $A \le $
Let $S =
\begin{cases}