Definition pure_readable_share (sh: Share.t) :=
  Share.glb Share.Lsh sh = Share.bot /\ readable_share sh.Definition rshare := sig pure_readable_share.Definition readable_part: forall (sh: Share.t) (rsh: readable_share sh), rshare.

Lemma readable_not_identity: forall sh P, readable_share sh -> identity sh -> P.