Notation val_inject:=Val.inject.
(*A value that is (if its a pointer) not dangling wrt m - a condition like this will probably be need to imposed on after-external return values (and thus also on the values returned by halted)*)
Definition val_valid (v:val) (m:mem):Prop :=
match v with Vptr b ofs => Mem.valid_block m b | _ => True
end.
(*memories that do not contain "dangling pointers"*)
Definition mem_wd m := Mem.inject_neutral (Mem.nextblock m) m.

Lemma  mem_wd_drop: forall m b lo hi p m' (DROP: Mem.drop_perm m b lo hi p = Some m')
(WDm: mem_wd m), Mem.valid_block m b -> mem_wd m'.