Question: The Association for Contemporary Music's leading members include what Russian composer of the early Soviet era, best known for his early futurist piano sonatas, orchestral episodes, and vocal music?

Context paragraphs:
Ingrid Haebler: Ingrid Haebler (born June 20, 1926 in Vienna, Austria) is an Austrian pianist.  She studied at the Salzburg Mozarteum, Vienna Music Academy, Geneva Conservatory and privately in Paris with Marguerite Long.  She toured worldwide.  She is best known for a series of recordings from the 1950s to 1980s.  Her complete set of Mozart's piano sonatas for the Denon label is still regarded as among the finest sets.  Haebler also recorded all of Mozart's piano concertos (most of them twice), often with her own cadenzas - and all of Schubert's sonatas.  She was one of several Austrian musicians to experiment early with period instruments, having recorded music of J. C. Bach on a fortepiano.  Her recordings of Mozart and Beethoven with violinist Henryk Szeryng are particularly prized.

Igor Boelza: Igor Fyodorovich Boelza (Игорь Фёдорович Бэлза; 8 February 1904 - 5 January 1994) was a Soviet music historian and composer who wrote 4 symphonies, 5 piano sonatas, 2 cello sonatas, a string quartet, and several film scores for Alexander Dovzhenko.  He was the father of Svyatoslav Belza, a showman and a TV personality.

János Négyesy: János Négyesy (or "Négyesy János", as should be written in Hungarian) was a Hungarian violinist with a particular interest in contemporary music.  He performed world premieres of numerous works, the first two books of the Freeman Etudes (etudes I–XVI and XVII–XXXII) by American composer John Cage among others.  He was also the first European violinist who recorded the complete Violin and Piano Sonatas of Charles Ives (with pianist Cornelius Cardew).  He is the author of a teaching and reference book on violin techniques, which was commissioned after he met Pierre Boulez at IRCAM in 1976.  In 1979, he joined the faculty of the University of California at San Diego.

Piano Sonata No. 21 (Beethoven): Beethoven's Piano Sonata No. 21 in C major, Op. 53, known as the Waldstein , is one of the three most notable sonatas of his middle period (the other two being the "Appassionata", Op. 57, and "Les Adieux", Op. 81a).  Completed in summer 1804 and surpassing Beethoven's previous piano sonatas in its scope, the "Waldstein " is a key early work of Beethoven's "Heroic" decade (1803–1812) and set a standard for piano composition in the grand manner.

Association for Contemporary Music: Association for Contemporary Music (ACM) (Russian: ACM - Ассоциация Современной Музыки , "ASM - Assotsiatsiya Sovremennoy Muzyki") was an alternative organization of Russian composers interested in avant-garde music.  It was founded by Nikolai Roslavets in 1923.  ACM ran concert series and published magazines promoting the modernist music of Mahler, Schoenberg, Berg, Webern, Krenek, and Hindemith, as well as the work of its members.  Its leading members were Dmitri Shostakovich, Nikolai Myaskovsky, Vissarion Shebalin, Alexander Mosolov, Gavriil Popov, and Vladimir Shcherbachev.  The organization's enthusiasm for avant-garde Western music and for experimentation met with opposition from the Russian Association of Proletarian Musicians (RAPM), which by the late 1920s had eclipsed the ACM in terms of cultural influence.  Both organizations existed until 23 April 1932, when they were abolished by the Decree on the Reformation of Literary and Artistic Organizations.

Alexander Mosolov: Alexander Vasilyevich Mosolov (Russian: Алекса́ндр Васи́льевич Мосо́лов , "Aleksandr Vasil'evič Mosolov" ; 11 August [O.S. 29 July] 1900  – 11 July 1973) was a Russian composer of the early Soviet era, known best for his early futurist piano sonatas, orchestral episodes, and vocal music.

Georgy Sviridov: Georgy Vasilyevich Sviridov (Russian: Гео́ргий Васи́льевич Свири́дов; his patronymic is also transliterated "Vasil'yevich", "Vasilievich", and "Vasil'evich") (December 16, 1915 – January 6, 1998) was a Russian neoromantic composer, active in the Soviet era.  He is most widely known for his choral music, strongly influenced by the traditional chant of the Russian Orthodox Church, as well as his orchestral works which often celebrate elements of Russian culture.  Sviridov employed, in his choral music especially, rich and dense harmonic textures, embracing a romantic-era tonality; his works would come to incorporate not only sacred elements of Russian church music, including vocal work for the basso profundo, but also display the influence of Eastern European folk music, 19th-century European romantic composers (especially Tchaikovsky), as well as neoromantic contemporaries outside of Russia.  He wrote musical settings of Russian Romantic-era poetry by poets such as Lermontov, Tyutchev and Blok.  Sviridov enjoyed critical acclaim for much of his career in the USSR.

Alexander Glazunov: Alexander Konstantinovich Glazunov (Russian: Алекса́ндр Константи́нович Глазуно́в , 10 August 1865 – 21 March 1936) was a Russian composer, music teacher, and conductor of the late Russian Romantic period.  He served as director of the Saint Petersburg Conservatory between 1905 and 1928 and was instrumental in the reorganization of the institute into the Petrograd Conservatory, then the Leningrad Conservatory, following the Bolshevik Revolution.  He continued heading the Conservatory until 1930, though he had left the Soviet Union in 1928 and did not return.  The best-known student under his tenure during the early Soviet years was Dmitri Shostakovich.

Sergei Prokofiev: Sergei Sergeyevich Prokofiev ( ; Russian: Сергей Сергеевич Прокофьев , "Sergej Sergejevič Prokofjev" ; 27 April 1891 – 5 March 1953) was a Soviet composer, pianist and conductor.  As the creator of acknowledged masterpieces across numerous musical genres, he is regarded as one of the major composers of the 20th century.  His works include such widely heard works as the March from "The Love for Three Oranges," the suite "Lieutenant Kijé", the ballet "Romeo and Juliet" – from which "Dance of the Knights" is taken – and "Peter and the Wolf."  Of the established forms and genres in which he worked, he created – excluding juvenilia – seven completed operas, seven symphonies, eight ballets, five piano concertos, two violin concertos, a cello concerto, a Symphony-Concerto for cello and orchestra, and nine completed piano sonatas.

Katerina Maier: Katerina Maier-Schiatti (fl.  c. 1800) was a Russian composer, the daughter of violinist and composer Luigi Schiatti who lived in Russia from 1760 and played in the court orchestra.  She published a set of three piano sonatas dedicated to Count Platon Zubov in St. Petersburg and a piano concerto in London around 1800.

Supporting paragraphs: Association for Contemporary Music Alexander Mosolov
Answer: Alexander Vasilyevich Mosolov