def build_pushforward_latents_step(get_observation_matrix_for_timestep,
                                   get_observation_noise_for_timestep):
  """
  """

  def pushforward_latents_step(_, latent_t_mean_cov):
    """Loop body fn to pushforward latents to observations at a time step."""
    t, latent_mean, latent_cov = latent_t_mean_cov

    observation_matrix = get_observation_matrix_for_timestep(t)
    observation_noise = get_observation_noise_for_timestep(t)
    observation_mean = _propagate_mean(latent_mean,
                                       observation_matrix,
                                       observation_noise)
    observation_cov = _propagate_cov(latent_cov,
                                     observation_matrix,
                                     observation_noise)

    return (observation_mean, observation_cov)

  return pushforward_latents_step