class EnumeratedIdentitySet implements Set<T> {

    static <T> List<T> removeNulls(T[] list) {
        int insertionSpot = 0;
        for (int i = 0; i < list.length; i++) {
            T element = list[i];
            if (element != null) {
                list[insertionSpot] = element;
                insertionSpot++;
            }
        }
        return Arrays.asList(list).subList(0, insertionSpot);
    }

    public  EnumeratedIdentitySet(Collection<? extends T> collection);
    public  EnumeratedIdentitySet();

}