def is_enriched(s1, s2, s3, s4):
    """
    Accessory function for further determine whether it is a co-enrichment after fisher-exact test.
    """
    total_1 = len(s1) + len(s2)
    total_2 = len(s3) + len(s4)
    if total_1 == 0 or total_2 == 0:
        return False
    if len(s1) / total_1 > len(s3) / total_2:
        return True
    else:
        return False
