Complex sentence: William Sethares described an overtones tuning that contains the fourth to ninth partials, omitting the first three partials (notes of the sequence of overtones) Its open notes do not form a major chord.
Split into simpler sentences: William Sethares described an overtones tuning that omits the first three partials (notes of the sequence of overtones). It also contains the note D, which is the note of the ninth partial of C. Its open notes do not form a major chord.