Local Open Scope nat_scope.
Local Open Scope pred.
Definition closed_wrt_modvars c (F: assert) : Prop :=
closed_wrt_vars (modifiedvars c) F.
Definition genv_symb_injective {F V} (ge: Genv.t F V) : extspec.injective_PTree block.

Lemma ext_join_unapprox : forall {Z} (z : Z) n g,
joins (ghost_fmap (approx n) (approx n) g) (Some (ghost_PCM.ext_ref z, NoneP) :: nil) ->
joins g (Some (ghost_PCM.ext_ref z, NoneP) :: nil).