(*  NOT TRUE, because readable doesn't constraint NoneP ... Lemma readable_VAL: forall w l, readable l (w_m w) <-> exists sh, (VALspec sh l * TT) w.  *)

Lemma approx_eq_i:
forall (P Q: pred rmap) (w: rmap),
(|> ! (P <=> Q)) w -> approx (level w) P = approx (level w) Q.