// Textbook fragment 02.14
public class PersonPairDirectory {
  // ... instance variables would go here ...
  public PersonPairDirectory() {/* default constructor goes here */}
  public void insert (Person person, Person other) {/* insert code goes here */}
  public Person findOther (Person person) { return null; } // stub for find
  public void remove (Person person, Person other) {/* remove code goes here */}
}