user: Question: What were the sets when Federer had 6 and a nadal of 13?
Columns: ['Year', 'Tournament', 'Surface', 'Round', 'Winner', 'Score', 'Length (H:MM)', 'Sets', 'Federer', 'Nadal']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'real', 'real']
Sample row: [2004.0, 'Miami', 'Hard', 'R32', 'Nadal', '6–3, 6–3', '1:10', '2/3', 0.0, 1.0]
SQL:

assistant: SELECT "Sets" FROM "Table" WHERE "Nadal" = 13.0 AND "Federer" = 6.0;