+\subsection{Foreign Ancestry}
+
+Only relevant if $\isforeign{L}$, in which case
+$\isforeign{C}$ and by Foreign Merge $\isforeign{R}$,
+so Totally Foreign Ancestry applies. $\qed$
+
+\subsection{Bases' Children}
+
+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.