/** Class specializing the generic merge template to union two sets */
public class UnionMerger extends Merger {
  protected void aIsLess(Object a, Sequence C) {
    C.insertLast(a);	// add a
  }
  protected void bothAreEqual(Object a, Object b, Sequence C) {
    C.insertLast(a);    // add a (but not its duplicate b)
  }
  protected void bIsLess(Object b, Sequence C) {
    C.insertLast(b);   // add b
  }
}