////   This file contains the C# code from Program 4.12 of//   "Data Structures and Algorithms//    with Object-Oriented Design Patterns in C#"//   by Bruno R. Preiss.////   Copyright (c) 2001--2002 by Bruno R. Preiss, P.Eng.  All rights reserved.////   http://www.brpreiss.com/books/opus6/programs/pgm04_12.txt//public class LinkedList{    protected Element head;    protected Element tail;    public sealed class Element    {	internal LinkedList list;	internal object datum;	internal Element next;	internal Element(	    LinkedList list, object datum, Element next)	{	    this.list = list;	    this.datum = datum;	    this.next = next;	}	public object Datum	    { get { return datum; } }	public Element Next	    { get { return next; } }	// ...    }    // ...}