Hint Extern 4 (value_fits _ _ _) =>
(rewrite ?proj_sumbool_is_true by auto;
rewrite ?proj_sumbool_is_false by auto;
repeat simplify_value_fits; auto) : prove_it_now.

Lemma intsigned_intrepr_bytesigned: forall i,
Int.signed (Int.repr (Byte.signed i)) = Byte.signed i.