instruction: what kind of aircraft is used on a flight from CLEVELAND to DALLAS
response: SELECT DISTINCT aircraft.aircraft_code FROM aircraft, airport_service AS AIRPORT_SERVICE_0, airport_service AS AIRPORT_SERVICE_1, city AS CITY_0, city AS CITY_1, equipment_sequence, flight WHERE CITY_0.city_code = AIRPORT_SERVICE_0.city_code AND CITY_0.city_name = 'CLEVELAND' AND CITY_1.city_code = AIRPORT_SERVICE_1.city_code AND CITY_1.city_name = 'DALLAS' AND equipment_sequence.aircraft_code = aircraft.aircraft_code AND flight.aircraft_code_sequence = equipment_sequence.aircraft_code_sequence AND flight.from_airport = AIRPORT_SERVICE_0.airport_code AND flight.to_airport = AIRPORT_SERVICE_1.airport_code