There are two main conventions for naming equal-tempered set classes. One, known as the Forte number, derives from Allen Forte, whose "The Structure of Atonal Music" (1973), is one of the first works in musical set theory. Forte provided each set class with a number of the form –, where indicates the cardinality of the set and is the ordinal number . Thus the chromatic trichord {0, 1, 2} belongs to set-class 3-1, indicating that it is the first three-note set class in Forte's list . The augmented trichord {0, 4, 8}, receives the label 3-12, which happens to be the last trichord in Forte's list.