Lemma decay_rewrite m m' : decay m m' <-> forall loc, (~valid_block m (fst loc) -> valid_block m' (fst loc) -> (forall k, access_at m' loc k = Some Freeable) \/ (forall k, access_at m' loc k = None)) /\ (valid_block m (fst loc) -> (forall k, (access_at m loc k = Some Freeable /\ access_at m' loc k = None)) \/ (forall k, access_at m loc k = access_at m' loc k)).