Hint Resolve writable_readable_share.
Definition extern_retainer := fst (Share.split Share.Lsh).
Definition Ews (* extern_write_share *) :=
Share.lub extern_retainer Share.Rsh.

Lemma sub_glb_bot:
forall r a c : share,
sepalg.join_sub a c ->
Share.glb r c = Share.bot ->
Share.glb r a = Share.bot.