////   This file contains the C++ code from Program 12.15 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/pgm12_15.cpp//MultisetAsLinkedList operator * (    MultisetAsLinkedList const& s, MultisetAsLinkedList const& t){    if (s.universeSize != t.universeSize)	throw invalid_argument ("mismatched sets");    MultisetAsLinkedList result (s.universeSize);    ListElement<unsigned int> const* p = s.list.Head();    ListElement<unsigned int> const* q = t.list.Head();    while (p && q)    {	int const diff = p->Datum () - q->Datum ();	if (diff == 0)	    result.list.Append (p->Datum ());	if (diff <= 0)	    p = p->Next ();	if (diff >= 0)	    q = q->Next ();    }    return result;}