This compositional variety is mediated by a highly redundant set structure, a second-order all-combinatorial set; each set form is hexachordally equivalent to or totally disjunct from fifteen other set forms, so that one-third of all the available set forms belong to a collection of sets which are hexachordally aggregate forming, that is, hexachordally identical.

On Igor Stravinsky's Movements. Perspectives of new music, Spring-Summer 1964