Ltac destruct_cjoin phi HH :=
  match goal with
   |   |- context [@proj1_sig rmap _ ?X] => destruct X as [phi HH]; simpl
   |  H: context [@proj1_sig rmap _ ?X] |- _ => destruct X as [phi HH]; simpl in H
  end.

Lemma split_top_neq: fst (Share.split Share.top) <> Share.top.