def score(prop, cluster):
    """
    Receives a proposition mention (mention, head_lemma, head_pos)
    and a cluster of proposition mentions, and returns a numeric value denoting the
    similarity between the mention to the cluster (% of same head lemma mentions in the cluster)
    :param prop: the mention
    :param cluster: the cluster
    :return: a numeric value denoting the similarity between the mention to the cluster
    """
    return len([other for other in cluster if other[1] == prop[1]]) / (1.0 * len(cluster))