Arguments readable_not_identity sh P _ _ : clear implicits.

Lemma join_comp_parts:
forall L R : Share.t,
Share.comp L = R ->
forall a b c : Share.t,
join a b c ->
(join (Share.glb L a) (Share.glb L b) (Share.glb L c) /\
join (Share.glb R a) (Share.glb R b) (Share.glb R c)).