public ExcelCellIndex Subtract(ExcelCellIndex other)
 {
     return(new ExcelCellIndex(RowIndex - other.RowIndex + 1, ColumnIndex - other.ColumnIndex + 1));
 }
 public ExcelCellIndex Add(ExcelCellIndex other)
 {
     return(new ExcelCellIndex(RowIndex + other.RowIndex - 1, ColumnIndex + other.ColumnIndex - 1));
 }