Ligeti's earliest works are often an extension of the musical language of Béla Bartók. Even his piano cycle "Musica ricercata" (1953), though written according to Ligeti with a "Cartesian" approach, in which he "regarded all the music I knew and loved as being... irrelevant", the piece has been described by one biographer as from a world very close to Bartók's set of piano works, "Mikrokosmos". Ligeti's set comprises eleven pieces in all. The work is based on a simple restriction: the first piece uses exclusively one pitch A, heard in multiple octaves, and only at the very end of the piece is a second note, D, heard. The second piece uses three notes (E, F, and G), the third piece uses four, and so on, so that in the final piece all twelve notes of the chromatic scale are present.