4. Bach, Versuch, II: 340–341, and [unpaginated] endplate. For a provocative study of the piece, see Heinrich Schenker, “Die Kunst der Improvisation,” in Schenker, Das Meisterwerk in der Musik, [I] (Munich, Vienna and Berlin: Drei Masken Verlag, 1925), 9–40; in English as “The Art of Improvisation,” tr. Richard Kramer, in The Masterwork in Music, ed. William Drabkin, I (Cambridge and New York: Cambridge University Press, 1994), 2–19. See also Annette Richards, The Free Fantasia and the Musical Picturesque, 42–43.