// Textbook fragment 02.16
public class PersonPairDirectoryGeneric<P extends Person> {
  // ... instance variables would go here ...
  public PersonPairDirectoryGeneric() { /* default constructor goes here */ }
  public void insert (P person, P other) { /* insert code goes here */ }
  public P findOther (P person) { return null; } // stub for find
  public void remove (P person, P other) { /* remove code goes here */ }
}