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 times3_times2: forall i,
0 <= Int.unsigned i < 256 ->
Int.and (Int.xor (times2 i) i) (Int.repr 255) = times3 i.