Groups of Objects: Collection enumerator class
	public class SequenceCollection : IEnumerator {    IntegerSequence sequence; int index;    public SequenceCollection(IntegerSequence Sequence)      {sequence=Sequence; index=sequence.Start-1;}    public bool MoveNext()      {++index; return (index>sequence.End)?false:true;}    public object Current{      get{         if (index<sequence.Start | index>sequence.End)            throw new InvalidOperationException(               "The selected IntegerSequence object is out of range");         return index;}    }    public void Reset() {index=sequence.Start-1;} }