user: Question: Name the engine with chassis of Maserati 250F and entrant of Luigi Piotti with year less than 1957
Columns: ['Year', 'Entrant', 'Chassis', 'Engine', 'Points']
Types: ['real', 'text', 'text', 'text', 'real']
Sample row: [1955.0, 'Scuderia Volpini', 'Arzani-Volpini', 'Maserati Straight-4', 0.0]
SQL:

assistant: SELECT "Engine" FROM "Table" WHERE "Chassis" = 'Maserati 250F' AND "Entrant" = 'Luigi Piotti' AND "Year" < 1957.0;