abstract class PersonList {
  //To calculate the number of descendents in this PersonList
  abstract int numDescendents();
}

class EmptyPL extends PersonList {
  // new EmptyPL().numDescendents() == 0
  //To calculate the number of descendents in this EmptyPL
  int numDescendents() {
    // ...
    return 0;
  }
}

class LargerPL extends PersonList {
 Person first;
 PersonList rest;

 LargerPL( Person first, PersonList rest ) {
   this.first = first;
   this.rest = rest;
 }

 //new LargerPL( new Someone( "Bob", new EmptyPL()), new EmptyPL()).numDescendents() == 1
 //new LargerPL( new Someone( "Bob", new LargerPL( new Someone("Kate", new EmptyPL()), new EmptyPL()) ),
 //    new LargerPL( new Someone( "Fred", new EmptyPL()), new EmptyPL())).numDescendents() == 3
 //To calculate the number of descendents in the LargerPL
 int numDescendents() {
   // ... this.first.PersonMethod() ... this.rest.PersonListMethod() ...
   return 1 + this.first.numDescendents() + this.rest.numDescendents();
 }
}

class JP {
  // new JP().iNowPronounce( new Someone("Jack",new EmptyPL()), new Someone("Jill",new EMptyPL()) ) -> 
  //  Jack.spouse == Jill; Jill.spouse == Jack
  //To join p1 and p2 in marriage
  void iNowProunounce( Person p1, Person p2 ) {
    // .. p1 .. p2
    p1.marryMe(p2);
    p2.marryMe(p1);
  }
}

abstract class Person {
   // To marry this person to another
   abstract void marryMe( Person to );

   // To add a kid of this Person
   abstract void addKid( String name );

   // To calculate the number of descendents of this Person
   abstract int numDescendents();
}

class Noone extends Person {
  // To marry this noone to another Person
  void marryMe( Person to ) {
  }

  // To add a kid of this Noone
  void addKid( String name ) {
  }

  // new Noone().numDescendents() == 0
  //To calculate the number of descendents of this Noone
  int numDescendents() {
    return 0;
  }
}

class Someone extends Person {
  String name;
  Person spouse;
  PersonList kids;

  Someone ( String name, PersonList kids ) {
   this.name = name;
   this.spouse = new Noone();
   this.kids = kids;
  }

  //Someone Tom = new Someone("Tom", new EmptyPL());
  //Someone mary = new Someone( "Mary", new EmptyPL() );
  // Tom.marryMe( mary );

  // new Someone("Tom", new EmptyPL()).marryMe(
  //     new Someone("Mary", new EmptyPL()) )
  //  Someone( "Tom", Noone() ,EmptyPL()) --> Someone( "Tom", Someone("Mary", Noone(), EmptyPL()) EmptyPL())
  // Tom.spouse -> Noone() ==> Tom.spouse == mary  
//To marry this Someone to another Person
  void marryMe( Person to ) {
    // ... this.name ... this.spouse.PersonMethod() ... this.kids.PersonListMethod() ... to
    this.spouse = to;
  }

  // Tom.addKid( "Jo" ) -> void
  // Someone( "Tom", mary, EmptyPL() ) -> Someone( "Tom", mary, LargerPL( Someone("Jo", EMptyPL() )
  // Tom.kids -> EmptyPL ==> Tom.kids -> LargerPL( Someone("Jo"..), EmptyPL)
  //To add a kid of this Someone
  void addKid( String name ) {
   // ... this.name ... this.spouse.PersonMethod() ... this.kids.PersonListMethod() ... name ...
   this.kids = new LargerPL( new Someone ( name, new EmptyPL() ), this.kids );
  }

  // Tom.numDescendents() == 1
  //new Someone("Bob", new LargerPL( new Someone("Fred", new EmptyPL()),
  //                      new LargerPL( new Someone("Sally", new LargerPL( new Someone("Dan",new EmptyPL()), new EmptyPL())),
  //                          new EmptyPL()))).numDescendents() == 3 
  // To calculate the number of descendents in this Someone
  int numDescendents() {
     // ... this.name ... this.spouse.PersonMethod() ... this.kids.PersonListMethod() ...
     return this.kids.numDescendents();
  }
}