text: public Ref3DPxg(int externalWorkbookNumber, SheetIdentifier sheetName, CellReference c): base(c){this.externalWorkbookNumber = externalWorkbookNumber;this.firstSheetName = sheetName.SheetId.Name;if (sheetName is SheetRangeIdentifier){this.lastSheetName = ((SheetRangeIdentifier)sheetName).LastSheetIdentifier.Name;}else{this.lastSheetName = null;}}