////   This file contains the C++ code from Program 9.12 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/pgm09_12.cpp//class NaryTree : public Tree{protected:    Object* key;    unsigned int const degree;    Array<NaryTree*> subtree;public:    NaryTree (unsigned int);    NaryTree (unsigned int, Object&);    ~NaryTree ();    Object& Key () const;    NaryTree& Subtree (unsigned int) const;    virtual void AttachKey (Object&);    virtual Object& DetachKey ();    virtual void AttachSubtree (unsigned int, NaryTree&);    virtual NaryTree& DetachSubtree (unsigned int);    // ...};