Question: The Advanced Tactical Fighter (ATF) was a demonstration and validation program undertaken by the United States Air Force, including the Soviet Sukhoi Su-27, a twin-engine supermaneuverable fighter aircraft designed by Sukhoi, it was designed to complement which aircraft?
Sentence (from "Advanced Tactical Fighter"): Lockheed and Northrop were selected in 1986 to develop the YF-22 and the YF-23 technology demonstrator aircraft.
Relevant evidence: No