import tensorflow as tf

        rew_t_ph = tf.placeholder(tf.float32, [None], name="reward")
        obs_tp1_input = make_obs_ph("obs_tp1")
        done_mask_ph = tf.placeholder(tf.float32, [None], name="done")
        importance_weights_ph = tf.placeholder(tf.float32, [None], name="weight")

        # q network evaluation
