Admitted.

Lemma xor_byte3_with_FSb: forall b0 b1 b2 b3 i,
Int.xor (word_to_int (b0, b1, b2, b3)) (Int.shl (Znth i tablesLL.FSb) (Int.repr 24))
= word_to_int (b0, b1, b2, (Int.xor b3 (Znth i tablesLL.FSb))).