MODULE Animals;
TYPE
  Animal = POINTER TO AnimalDesc;
  AnimalDesc = RECORD END;

  Cat = POINTER TO CatDesc;
  CatDesc = RECORD (AnimalDesc) END;

  Dog = POINTER TO DogDesc;
  DogDesc = RECORD (AnimalDesc) END;

  Lab = POINTER TO LabDesc;
  LabDesc = RECORD (DogDesc) END;

  Collie = POINTER TO CollieDesc;
  CollieDesc = RECORD (DogDesc) END;

END Animals.