At the invitation of Wolfgang Steinecke, Adorno took part in the Darmstadt Summer Courses for New Music in Kranichstein from 1951 to 1958. Yet conflicts between the so-called Darmstadt school, which included composers like Pierre Boulez, Karlheinz Stockhausen, Luigi Nono, Bruno Maderna, Karel Goeyvaerts, Luciano Berio and Gottfried Michael Koenig, soon arose, receiving explicit expression in Adorno's 1954 lecture, "The Aging of the New Music", where he argued that atonality's freedom was being restricted to serialism in much the same way as it was once restricted by twelve-tone technique. With his friend Eduard Steuermann, Adorno feared that music was being sacrificed to stubborn rationalization. During this time Adorno not only produced a significant series of notes on Beethoven (which was never completed and only published posthumously), but also published "Mahler: A Musical Physiognomy" in 1960. In his 1961 return to Kranichstein, Adorno called for what he termed a "musique informelle", which would possess the ability "really and truly to be what it is, without the ideological pretense of being something else. Or rather, to admit frankly the fact of non-identity and to follow through its logic to the end."