Ltac eta5 HH :=
  let Hnew := fresh in match type of HH with
  | ?f = (fun a1 a2 a3 a4 a5 => ?e) =>
    assert (forall a1 a2 a3 a4 a5, f a1 a2 a3 a4 a5 = e) as Hnew by (intro; rewrite HH; reflexivity)
  end;
  clear HH; rename Hnew into HH.

Lemma mbed_tls_final_fround_sublist: forall i s ks, 0 <= i <= Zlength ks - 4 -> mbed_tls_final_fround s ks i = mbed_tls_final_fround s (sublist i (i+4) ks) 0.