Definition update_rounds (non_empty_additional: bool): Z :=
  if non_empty_additional then 2 else 1.

Lemma HMAC_DRBG_update_round_incremental: forall key V initial_state_abs contents n, (key, V) = HMAC_DRBG_update_round HMAC256 contents (hmac256drbgabs_key initial_state_abs) (hmac256drbgabs_value initial_state_abs) n -> (HMAC256 (V ++ Byte.repr (Z.of_nat n) :: contents) key, HMAC256 V (HMAC256 (V ++ Byte.repr (Z.of_nat n) :: contents) key)) = HMAC_DRBG_update_round HMAC256 contents (hmac256drbgabs_key initial_state_abs) (hmac256drbgabs_value initial_state_abs) (n + 1).