Definition genvs_domain_eq {F1 F2 V1 V2: Type} (ge1: Genv.t F1 V1) (ge2: Genv.t F2 V2) :=
  (forall b, fst (genv2blocks ge1) b <-> fst (genv2blocks ge2) b) /\
  (forall b, snd (genv2blocks ge1) b <-> snd (genv2blocks ge2) b).

Lemma unchanged_on_perm_intersection: forall m m' U (Fwd: mem_forward m m'), Mem.unchanged_on U m m' <-> Mem.unchanged_on (fun b z => U b z /\ Mem.perm m b z Max Nonempty) m m'.