Busoni also drew inspiration from North American indigenous tribal melodies drawn from the studies of Natalie Curtis, which informed his "Indian Fantasy" for piano and orchestra of 1913 and two books of solo piano sketches, "Indian Diary". In 1917, Busoni wrote the one-act opera "Arlecchino" (1917) as a companion piece for his revision of "Turandot" as an opera. He began serious work on his opera "Doktor Faust" in 1916, leaving it incomplete at his death. It was then finished by his student Philipp Jarnach, who worked with Busoni's sketches as he knew of them. In the 1980s Antony Beaumont created an expanded and improved completion by drawing on material to which Jarnach did not have access; Joseph Horowitz has described the Beaumont completion as "longer, more adventurous and perhaps less good."