The most fateful of the new generation was Ludwig van Beethoven, who launched his numbered works in 1794 with a set of three piano trios, which remain in the repertoire. Somewhat younger than the others, though equally accomplished because of his youthful study under Mozart and his native virtuosity, was Johann Nepomuk Hummel. Hummel studied under Haydn as well; he was a friend to Beethoven and Franz Schubert. He concentrated more on the piano than any other instrument, and his time in London in 1791 and 1792 generated the composition and publication in 1793 of three piano sonatas, opus 2, which idiomatically used Mozart's techniques of avoiding the expected cadence, and Clementi's sometimes modally uncertain virtuoso figuration. Taken together, these composers can be seen as the vanguard of a broad change in style and the center of music. They studied one another's works, copied one another's gestures in music, and on occasion behaved like quarrelsome rivals.