def is_canopy(k,C_less_than):
    """
    A check used by the Hierarchy class to determine whether
    a given cluster index is a top-level cluster among
    a given subset of clusters.
    """
    is_cpy = True
    for j in C_less_than:
        if (len(C_less_than[j])>1) and (k in C_less_than[j]):
            is_cpy = False
    return is_cpy