[7] This family of chords is mentioned by Bauer-Mengelberg and Ferentz, "On Eleven-Interval Twelve-Tone Rows," 97, n. 4, and described in more detail by Morris and Starr, "The Structure of All-Interval Series," 370. Because they define their operations on strings of pitch classes rather than intervals, Morris and Starr refer to such chords as "R-invariant."