Definition size_chunk_nat (chunk: memory_chunk) : nat :=
  nat_of_Z(size_chunk chunk).

(* Specifications: *)
Lemma size_chunk_conv: forall chunk, size_chunk chunk = Z.of_nat (size_chunk_nat chunk).
Lemma size_chunk_nat_pos: forall chunk, exists n, size_chunk_nat chunk = S n.
Lemma size_chunk_Mptr: size_chunk Mptr = if Archi.ptr64 then 8 else 4.