Most important is the fact that Mozart revised his symphony (see above). As Zaslaw says, this "demonstrates that symphony was performed, for Mozart would hardly have gone to the trouble of adding the clarinets and rewriting the flutes and oboes to accommodate them, had he not had a specific performance in view." The orchestra for the 1791 Vienna concert included the clarinetist brothers Anton and Johann Nepomuk Stadler; which, as Zaslaw points out, limits the possibilities to just the 39th and 40th symphonies.