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 calc_FT2_expose_bytes: forall i,
0 <= i < 256 ->
calc_FT2 i = word_to_int (FT0b2 i, FT0b3 i, FT0b0 i, FT0b1 i).