import java.util.*;
class SetOperations { 
    public static void main (String[] args) {
	TreeSet s = new TreeSet();
	s.add("mno");	s.add("jkl");	s.add("ghi");
	TreeSet t = new TreeSet();
	t.add("def");	t.add("abc");	t.add("ghi");

	// Add all of the elements of t to s (set union)
	s.addAll(t);          

	// next statement prints [abc, def, ghi, jkl, mno]
	System.out.println(s);

	// Remove all elements of t from s (set difference)
	s.removeAll(t);          

	// next statement prints [jkl, mno]
	System.out.println(s);
    }
}