Hint Rewrite Zlength_intlist_to_bytelist : sublist.

Lemma big_endian_integer4:
forall c0 c1 c2 c3,
big_endian_integer (c0::c1::c2::c3::nil) =
Int.or (Int.shl (Int.repr (Byte.unsigned c0)) (Int.repr 24))
(Int.or (Int.shl (Int.repr (Byte.unsigned c1)) (Int.repr 16))
(Int.or (Int.shl (Int.repr (Byte.unsigned c2)) (Int.repr 8))
(Int.repr (Byte.unsigned c3)))).