[6] The Q operation is discussed by Morris and Starr, "The Structure of All-Interval Series," 365-366. All-interval chords also are closed under the operation M5, or multiplication of each interval by 5 modulo 12. See Bauer-Mengelberg and Ferentz, "On Eleven-Interval Twelve-Tone Rows," 99, n. 6, and Morris and Starr, "The Structure of All-Interval Series," 365-366. RI- and QI-invariant all-interval chords (discussed below) are closed under an operation by which the order positions of the intervals 3 and 9 are exchanged. See Mead, "Twelve-Tone Composition."