Question: HPSCHD is a composition by which music theorist and writer?
Context: Brazilian composer and music theorist, whose main interest has been the vivid interaction between composition and culture, including the political aspects of it, namely, composition as a way of resisting cultural colonization.  He has published books and articles on subjects such as the theory and pedagogy of musical composition, analysis and history of Brazilian contemporary music, analysis of Brazilian popular songs, and the possible dialogue between music, psychoanalysis and cultural semantics.  A member of the Brazilian Academy of Music (created by Heitor Villa-Lobos in 1945), he has received along the last decades more than twenty prizes and commissions.  He belongs to the second generation of the movement initiated by the ‘Group of Composers of Bahia’ that was formed in 1966, launching a one-line manifesto “In principle, we are against all and every asserted principle”.  The manifesto also implies that all suggestions are valid and acceptable, and this inclusivity reflects the cultural diversity and relativity of Bahia - a society created by the encounter and conflict of three civilizations (Europe, Africa and Native American).  Since 1992 his compositional interests addressed the rhythmic tradition of Afro-Bahian candomblé, creating universes of hybridization and contradiction, non-sequitur and humor, involving Afro-Bahian and Avant-Garde contexts and ideas.  He has mentored a new generation of Brazilian composers such as Guilherme Bertissolo, Paulo Rios Filho, Alex Pochat, Tulio Augusto, Vinicius Amaro and Danniel Ferraz. John Milton Cage Jr. (September 5, 1912 – August 12, 1992) was an American composer, music theorist, writer, philosopher, and artist.  A pioneer of indeterminacy in music, electroacoustic music, and non-standard use of musical instruments, Cage was one of the leading figures of the post-war avant-garde.  Critics have lauded him as one of the most influential composers of the 20th century.  He was also instrumental in the development of modern dance, mostly through his association with choreographer Merce Cunningham, who was also Cage's romantic partner for most of their lives. Joseph Moiseyevich Schillinger (Russian: Иосиф Моисеевич Шиллингер, 31 August 1895 – 23 March 1943) was a composer, music theorist, and composition teacher who originated the Schillinger System of Musical Composition.  He was born in Kharkiv, in the Kharkov Governorate of the Russian Empire (present-day Ukraine) and died in New York City. HPSCHD (pronounced as acronym: eɪtʃ-piː-ɛs-siː-eɪtʃ-di:, although Cage himself said the title is "Harpsichord"), is a composition for harpsichord and computer-generated sounds by American avant-garde composers John Cage (1912–1992) and Lejaren Hiller (1924–1994).  It was written between 1967 and 1969 and was premiered on May 16, 1969, at the Experimental Music Studios at the University of Illinois at Urbana–Champaign. Gioseffo Zarlino (31 January or 22 March 1517 – 4 February 1590) was an Italian music theorist and composer of the Renaissance.  He was possibly the most famous European music theorist between Aristoxenus and Rameau, and made a large contribution to the theory of counterpoint as well as to musical tuning. Josep Soler i Sardà (born 25 March 1935 in Vilafranca del Penedès) is a Spanish composer, writer and music theorist, one of the main Catalan members of the Generación del 51.  He studied composition and orchestration with Cristòfor Taltabull, and was also a pupil of René Leibowitz in Paris. Roland Carroll Jordan, Jr (born 1938) is an American composer and music theorist.  He studied in Texas and Pennsylvania before receiving his Ph.D. from Washington University in St. Louis, where he taught theory and composition for three decades.  As a composer, Jordan has written for both large ensembles and chamber groups, and as a music theorist, he has explored the uses of phenomenological methodology and structuralist/post-structuralist theory. Miguel Ángel Roig-Francolí (born 1953) is a Spanish/American composer, music theorist, and pedagogue.  His 1980 "Cinco piezas para orquesta" ("Five Pieces for Orchestra"), commissioned by Radio Nacional de España and written in a postmodern, neotonal style, won first prize in the National Composition Competition of the Spanish "Jeunesses Musicales" in 1981 and second prize at the UNESCO International Rostrum of Composers in 1982, and continues to be widely performed in Spain.  His later compositions often have spiritual themes and are based on sacred texts and the melodies of Gregorian chant.  In 2016 he won the American Prize in Composition (Band/Wind Ensemble Division) for Perseus, for symphonic band.  An expert on Renaissance composers Tomás de Santa María, Antonio de Cabezón, and Tomás Luis de Victoria, he has published numerous scholarly articles and monographs and two textbooks.  Roig-Francolí is a Distinguished Teaching Professor of Music Theory and Composition at the University of Cincinnati – College-Conservatory of Music. Josef Matthias Hauer (March 19, 1883 – September 22, 1959) was an Austrian composer and music theorist.  He is most famous for developing, independent of and a year or two before Arnold Schoenberg, a method for composing with all 12 notes of the chromatic scale.  Hauer was also an important early theorist of twelve-tone music and composition. Marchetto da Padova (Marchettus of Padua; fl.  1305 – 1319) was an Italian music theorist and composer of the late medieval era.  His innovations in notation of time-values were fundamental to the music of the Italian ars nova, as was his work on defining the modes and refining tuning.  In addition, he was the first music theorist to discuss chromaticism.
Answer: John Milton Cage Jr.