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

Lemma alloc_decay: forall m lo hi m1 b1, Mem.alloc m lo hi = (m1,b1) -> decay m m1.