/// <summary> Removes a subject from the list of subjects related to this item </summary>
 /// <param name="Subject"> Subject to remove </param>
 public void Remove_Subject(Subject_Info Subject)
 {
     if ((subjects != null) && (subjects.Contains(Subject)))
         subjects.Remove(Subject);
 }
        /// <summary> Add an existing subject to this digital resource </summary>
        /// <param name="Subject"> Subject to add to this resource </param>
        public void Add_Subject(Subject_Info Subject)
        {
            if (subjects == null)
                subjects = new List<Subject_Info>();

            subjects.Add(Subject);
        }