WITH
SET [a] AS [Product].[Subcategory].Levels(1).Members
SET [b] AS [Date].[Calendar].Levels(1).Members
SELECT
     Order([a],[b].Item(0), BDESC ) ON ROWS,
     Order([b],[a].Item(0), BDESC  ) ON COLUMNS
FROM [Adventure Works] ;

works the same as:

WITH
SET [RowSet]    AS [Product].[Subcategory].Levels(1).Members
SET [ColumnSet] AS [Date].[Calendar].Levels(1).Members
SELECT
     Order( [RowSet], [ColumnSet].Item(0), BDESC ) ON ROWS,
     Order([ColumnSet],[RowSet].Item(0), BDESC  ) ON COLUMNS
FROM [Adventure Works];