import tensorflow as tf

    head_emb = tf.nn.dropout(head_emb, self.lexical_dropout) # [num_sentences, max_sentence_length, emb]

    text_len_mask = tf.sequence_mask(text_len, maxlen=max_sentence_length) # [num_sentence, max_sentence_length]

    context_outputs = self.lstm_contextualize(context_emb, text_len, text_len_mask) # [num_words, emb]
    num_words = util.shape(context_outputs, 0)

    genre_emb = tf.gather(tf.get_variable("genre_embeddings", [len(self.genres), self.config["feature_size"]]), genre) # [emb]

    sentence_indices = tf.tile(tf.expand_dims(tf.range(num_sentences), 1), [1, max_sentence_length]) # [num_sentences, max_sentence_length]
    flattened_sentence_indices = self.flatten_emb_by_sentence(sentence_indices, text_len_mask) # [num_words]
    flattened_head_emb = self.flatten_emb_by_sentence(head_emb, text_len_mask) # [num_words]

    candidate_starts = tf.tile(tf.expand_dims(tf.range(num_words), 1), [1, self.max_span_width]) # [num_words, max_span_width]
    candidate_ends = candidate_starts + tf.expand_dims(tf.range(self.max_span_width), 0) # [num_words, max_span_width]
    candidate_start_sentence_indices = tf.gather(flattened_sentence_indices, candidate_starts) # [num_words, max_span_width]
    candidate_end_sentence_indices = tf.gather(flattened_sentence_indices, tf.minimum(candidate_ends, num_words - 1)) # [num_words, max_span_width]
    candidate_mask = tf.logical_and(candidate_ends < num_words, tf.equal(candidate_start_sentence_indices, candidate_end_sentence_indices)) # [num_words, max_span_width]
    flattened_candidate_mask = tf.reshape(candidate_mask, [-1]) # [num_words * max_span_width]
    candidate_starts = tf.boolean_mask(tf.reshape(candidate_starts, [-1]), flattened_candidate_mask) # [num_candidates]
    candidate_ends = tf.boolean_mask(tf.reshape(candidate_ends, [-1]), flattened_candidate_mask) # [num_candidates]
    candidate_sentence_indices = tf.boolean_mask(tf.reshape(candidate_start_sentence_indices, [-1]), flattened_candidate_mask) # [num_candidates]

    candidate_cluster_ids = self.get_candidate_labels(candidate_starts, candidate_ends, gold_starts, gold_ends, cluster_ids) # [num_candidates]

    candidate_span_emb = self.get_span_emb(flattened_head_emb, context_outputs, candidate_starts, candidate_ends) # [num_candidates, emb]
    candidate_mention_scores =  self.get_mention_scores(candidate_span_emb) # [k, 1]
    candidate_mention_scores = tf.squeeze(candidate_mention_scores, 1) # [k]

    k = tf.to_int32(tf.floor(tf.to_float(tf.shape(context_outputs)[0]) * self.config["top_span_ratio"]))
