Ancestors: $ D \le C \equiv D \le L $.
Contents: $ D \isin C \equiv D \isin L \lor f $
-so $ D \isin C \equiv D \isin L $.
+so $ D \isin C \equiv D \isin L $, i.e. $ C \zhaspatch P $.
+By $\haspatch$ for $L$, $\exists_{F \in \py} F \le L$
+and this $F$ is also $\le C$. So $\haspatch$.
So:
\[ L \haspatch \p \implies C \haspatch \p \]