def get_mention_token_dist(m1, m2):
    """ Returns distance in tokens between two mentions """
    succ = m1.tokens[0].doc_index < m2.tokens[0].doc_index
    first = m1 if succ else m2
    second = m2 if succ else m1

    return max(0, second.tokens[0].doc_index - first.tokens[-1].doc_index)