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 msem_decay: forall C (Sem: MemSem C) c m c' m', corestep (csem Sem) c m c' m' -> decay m m'.