/**
 *
 * @param sheetIden may be <code>null</code>
 * @param part1
 * @param part2 may be <code>null</code>
 */
        private ParseNode CreateAreaRefParseNode(SheetIdentifier sheetIden, SimpleRangePart part1,
                SimpleRangePart part2)
        {

            int extIx;
            if (sheetIden == null)
            {
                extIx = Int32.MinValue;
            }
            else
            {
                String sName = sheetIden.SheetID.Name;
                if (sheetIden.BookName == null)
                {
                    extIx = _book.GetExternalSheetIndex(sName);
                }
                else
                {
                    extIx = _book.GetExternalSheetIndex(sheetIden.BookName, sName);
                }
            }
            Ptg ptg;
            if (part2 == null)
            {
                CellReference cr = part1.getCellReference();
                if (sheetIden == null)
                {
                    ptg = new RefPtg(cr);
                }
                else
                {
                    ptg = new Ref3DPtg(cr, extIx);
                }
            }
            else
            {
                AreaReference areaRef = CreateAreaRef(part1, part2);

                if (sheetIden == null)
                {
                    ptg = new AreaPtg(areaRef);
                }
                else
                {
                    ptg = new Area3DPtg(areaRef, extIx);
                }
            }
            return new ParseNode(ptg);
        }
        public LazyRefEval(Ref3DPtg ptg, SheetRefEvaluator sre)
            : base(ptg.Row, ptg.Column)
        {

            _evaluator = sre;
        }