+
+\subsection{Bases' Children}
+
+We need to consider this for $D=L$ and also for $D=R$ ($R \in \set
+R$).
+
+For $D=L$, if $L \in \pn$ then $C \in \pn$, OK; whereas if
+$L \not \in \pn$ Bases' Children is inapplicable.
+
+For $D=R$,
+xxx up to here?
+
+If $L \in \py, R \in \py$: not applicable for either $D=L$ or $D=R$.
+
+If $L \in \py, R \in \pn$: not applicable for $L$, OK for $R$.
+
+Other possibilities for $L \in \py$ are excluded by Tip Merge.
+
+If $L \in \pn, R \in \pn$: satisfied for both $L$ and $R$.
+
+If $L \in \pn, R \in \foreign$: satisfied for $L$, not applicable for
+$R$.
+
+If $L \in \pn, R \in \pqy$: satisfied for $L$, not applicable for
+$R$.
+
+Other possibilities for $L \in \pn$ are excluded by Base Merge.
+
+If $L \in \foreign$: not applicable for $L$; nor for $R$, by Foreign Merges.
+
+