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 bot_unreadable: ~readable_share Share.bot.
Definition pure_readable_share (sh: Share.t) :=
Share.glb Share.Lsh sh = Share.bot /\ readable_share sh.