Definition perm_order''_dec : forall (op op' : option permission),
{Mem.perm_order'' op op'} + {~ Mem.perm_order'' op op'}.

(* Specifications: *)
Lemma alloc_decay:
forall m lo hi m1 b1, Mem.alloc m lo hi = (m1,b1) -> decay m m1.
Lemma free_decay: forall m b lo hi m', Mem.free m b lo hi = Some m' -> decay m m'.
Lemma msem_decay:
forall C (Sem: MemSem C) c m c' m',
corestep (csem Sem)  c m c' m' ->
decay m m'.