////   This file contains the C++ code from Program 16.1 of//   "Data Structures and Algorithms//    with Object-Oriented Design Patterns in C++"//   by Bruno R. Preiss.////   Copyright (c) 1998 by Bruno R. Preiss, P.Eng.  All rights reserved.////   http://www.pads.uwaterloo.ca/Bruno.Preiss/books/opus4/programs/pgm16_01.cpp//class Vertex : public Object{public:    typedef unsigned int Number;protected:    Number number;public:    Vertex (Number);    virtual operator Number () const;    // ...};