Definition FT0b0(i: Z): int := GF_ops_LL.times2 (Znth i FSb).
Definition FT0b1(i: Z): int := Znth i FSb.
Definition FT0b2(i: Z): int := Znth i FSb.
Definition FT0b3(i: Z): int := GF_ops_LL.times3 (Znth i FSb).
(* Note: according to calc_FT0, it should FT0b3 is (Int.and (Int.xor (GF_ops_LL.times2 (Znth i FSb)) (Znth i FSb)) (Int.repr 255)) but we prefer to use an equivalent "medium-level" formulation *)

Lemma split_quad_eq': forall {T : Type} (c0 c1 c2 c3 c0' c1' c2' c3' : T),
c0 = c0' -> c1 = c1' -> c2 = c2' -> c3 = c3' -> (c0, (c1, (c2, c3))) = (c0', (c1', (c2', c3'))).