////   This file contains the C++ code from Program 7.1 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/pgm07_01.cpp//class Position : public Iterator{};class List : public virtual SearchableContainer{public:    virtual Object& operator [] (unsigned int) const = 0;    virtual Object& operator [] (Position const&) const = 0;    virtual Position& FindPosition (Object const&) const = 0;    virtual void Withdraw (Position const&) = 0;};class OrderedList : public virtual List{public:    virtual void InsertAfter (Position const&, Object&) = 0;    virtual void InsertBefore (Position const&, Object&) = 0;};