destruct B as (((q0, q1), q2), q3). simpl.
rewrite SixteenByte2ValList_char, app_nil_r. trivial.
Qed.

Lemma SixteenByte2ValList_Zlength C: 16 = Zlength (SixteenByte2ValList C).
destruct C as (((q0, q1), q2), q3). unfold SixteenByte2ValList.