culminated in Piano Sonata, Op. 1 (1907–1908); it is one of the most formidable "first" works ever written. Berg studied with Schoenberg for six years until 1911. Among Schoenberg's teaching was the idea that the unity of a musical composition depends upon all its aspects being derived from a single basic idea; this idea was later known as developing variation. Berg passed this on to his students, one of whom, Theodor W. Adorno, stated: "The main principle he conveyed was that of variation: everything was supposed to develop out of something else and yet be intrinsically different". The Piano Sonata is an example—the whole composition is derived from the work's opening quartal gesture and its opening phrase. Innovation Berg was a part of Vienna's cultural elite during the heady fin de siècle period. His circle included the musicians Alexander von Zemlinsky and Franz Schreker, the painter Gustav Klimt, the writer and satirist Karl Kraus, the architect Adolf Loos, and the poet Peter Altenberg. In 1906 Berg met the singer (1885–1976), daughter of a wealthy family (rumoured to be in fact the illegitimate daughter of Emperor Franz Joseph I from his liaison with Anna Nahowski). Despite the outward hostility of her family, the couple married on 3 May 1911. In 1913 two of Berg's Altenberg Lieder (1912) were premièred in Vienna, conducted by Schoenberg in the infamous Skandalkonzert. Settings of aphoristic poetic utterances, the songs are accompanied by a very large orchestra. The performance caused a riot, and had to be halted. Berg effectively withdrew the work, and it was not performed in full until 1952. The full score remained unpublished until 1966. From 1915 to 1918 Berg served in the Austro-Hungarian Army. During a period of leave in 1917 he accelerated work on his first opera, Wozzeck. After the end of World War I, he settled again in Vienna, where he taught private pupils. He also helped Schoenberg run his Society for Private Musical Performances, which sought to create the ideal environment for the exploration and appreciation of unfamiliar new music by means of open rehearsals, repeat performances, and the exclusion of professional critics. Berg had a particular interest in the number 23, using it to structure several works. Various suggestions have been made as to the reason for this interest: that he took it from the biorhythms theory of Wilhelm Fliess, in which a 23-day cycle is considered significant,