Definition isGlobalBlock {F V : Type} (ge : Genv.t F V) :=
  fun b => (fst (genv2blocksBool ge)) b || (snd (genv2blocksBool ge)) b.

Lemma replace_externs_meminj_preserves_globals: forall {F V} (ge: Genv.t F V) nu (PG: meminj_preserves_globals ge (extern_of nu) /\ (forall b, isGlobalBlock ge b = true -> frgnBlocksSrc nu b = true)) mu fSrc fTgt (Hyp: mu = replace_externs nu fSrc fTgt) (FRG: forall b, frgnBlocksSrc nu b = true -> fSrc b = true), meminj_preserves_globals ge (extern_of mu) /\ (forall b, isGlobalBlock ge b = true -> frgnBlocksSrc mu b = true).