From June 1914 to January 1915, Busoni was in Berlin. As a native of a neutral country (Italy) living in Germany, Busoni was not greatly concerned, at first, by the outbreak of war. During this period, he began to work seriously on the libretto for his proposed opera "Doktor Faust". In January 1915 he left for a concert tour of the US, which was to be his last visit there. During this time he continued work on his Bach edition, including his version of the "Goldberg Variations". Upon the composer's return to Europe, Italy had entered the war. Busoni therefore chose to base himself from 1915 in Switzerland. In Zurich, he found local supporters in Volkmar Andreae (conductor of the Tonhalle Orchestra) and Philipp Jarnach. His friend José Vianna da Motta also taught piano in Geneva at this time. Andreae arranged for Busoni to give concerts with his orchestra. Jarnach, who was 23 when he met Busoni, in 1915, became Busoni's indispensable assistant, among other things preparing piano scores of his operas; Busoni referred to him as his "". While in America, Busoni had carried out further work on "Doktor Faust", and had written the libretto of his one-act opera "Arlecchino". He completed it in Zurich and, to provide a full evening at the theatre, reworked his earlier "Turandot" into a one-act piece. The two were premiered together in Zurich in May 1917.