import java.util.*;
   public class TreeSetWithOps extends TreeSet
   {
      public Set setIntersection(Set set2)
      {
         Set answer = new TreeSet();
         Iterator it = this.iterator();
         while(it.hasNext())
         {
            Object temp = it.next();
            if(set2.contains(temp))
               answer.add(temp);
         }
         return answer;
      }
      public Set setUnion(Set set2)
      {
         Set answer = new TreeSet();
         Iterator it1 = this.iterator();
         Iterator it2 = set2.iterator();
         while(it1.hasNext())
            answer.add(it1.next());
         while(it2.hasNext())
            answer.add(it2.next());
         return answer;
      }
      public Set setDifference(Set set2)
      {
         Set answer = new TreeSet();
         Iterator it = this.iterator();
         while(it.hasNext())
         {
            Object temp = it.next();
            if(!set2.contains(temp))
               answer.add(temp);
         }
         return answer;
      }
      public boolean isSubset(Set set2)
      {
         return set2.equals(setIntersection(set2));
      }
      public boolean isProperSubset(Set set2)
      {
         return set2.size() < this.size() && isSubset(set2);
      }
   }