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.