Definition decay m_before m_after := forall b ofs,
      (~Mem.valid_block m_before b ->
       Mem.valid_block m_after b ->
       (forall k, Maps.PMap.get b (Mem.mem_access m_after) ofs k = Some Freeable)
       \/ (forall k, Maps.PMap.get b (Mem.mem_access m_after) ofs k = None)) /\
      (Mem.valid_block m_before b ->
       (forall k,
           (Maps.PMap.get b (Mem.mem_access m_before) ofs k = Some Freeable /\
            Maps.PMap.get b (Mem.mem_access m_after) ofs k = None)) \/
       (forall k, Maps.PMap.get b (Mem.mem_access m_before) ofs k =
             Maps.PMap.get b (Mem.mem_access m_after) ofs k)).Definition strong_decay m_before m_after := forall b ofs,
       (~Mem.valid_block m_before b ->
       Mem.valid_block m_after b ->
       (forall k, Maps.PMap.get b (Mem.mem_access m_after) ofs k = Some Freeable)
       \/ (forall k, Maps.PMap.get b (Mem.mem_access m_after) ofs k = None)) /\
      (Mem.valid_block m_before b ->
       (forall k, Maps.PMap.get b (Mem.mem_access m_before) ofs k =
             Maps.PMap.get b (Mem.mem_access m_after) ofs k)).

Lemma decay_trans : forall m m' m'', (forall b, Mem.valid_block m b -> Mem.valid_block m' b) -> decay m m' -> decay m' m'' -> decay m m''.