Question: Which of russian composer Igor Stravinsky's works was once conducted by Eduard Flipse, and featured avant-garde natured music?
Sentence (from "Concerto for Two Pianos (Stravinsky)"): It was finished on November 9, 1935 and, together with his Sonata for Two Pianos, is considered nowadays as one of his major compositions for piano during his neoclassical period.
Relevant evidence: No