public HashSet<T> union(HashSet<T> u) {
HashSet<T> n = new HashSet<T>(this);
Iterator<T> e = u.iterator();
while (e.hasNext()) n.add(e.next());
return n;
}
/**
* Add the elements of another HashSet to this HashSet.
*
* @param hs the HashSet from which the new elements are obtained
*/
public void add(HashSet<T> hs) {
Iterator<T> e = hs.iterator();
while (e.hasNext()) this.add(e.next());
}