def __filter_vertices(k, coreness, *args, **kwargs):
    """
    .. function filter_vertices(k, coreness)

    Filters coreness mapping for vertex ids in k-core >= k.

    :param k: minimum k-core
    :param list coreness: vertex -> k-core mapping
    :return: vertices in k-core
    """
    return list(filter(lambda i: coreness[i] >= k, range(len(coreness))))