Definition compat_pointer_chunks (chunk1 chunk2: memory_chunk) : Prop :=
  match chunk1, chunk2 with
  | (Mint32 | Many32), (Mint32 | Many32) => True
  | (Mint64 | Many64), (Mint64 | Many64) => True
  | _, _ => False
  end.

Theorem range_perm_drop_2: forall m b lo hi p, range_perm m b lo hi Cur Freeable -> {m' | drop_perm m b lo hi p = Some m' }.