Stockhausen had been interested for several years in writing something for the Kontarsky piano duo, and by early 1969 he had become determined to do so.) On a flight from the Northeastern United States to Los Angeles in September 1969 or shortly before, he had sketched "a kind of theater piece for two pianos" titled "Vision", and in March 1970 began to work out a score, but broke off after just three pages. During an automobile trip from Madison, Connecticut to Boston, a melody came to Stockhausen, along with the idea of expanding such a musical figure over a very long period of time—fifty or sixty minutes. He jotted the melody down on an envelope at that time, but it only occurred to him after having abandoned "Vision" that this might become the basis for his new two-piano composition. Stockhausen later recalled that this was early in September 1969, but the sketch is in fact dated 26 February.