AN equivaleNce class is a subset whose elemeNts are related to each other by aNequivaleNce relatioN. The equivaleNce classes of a set uNder some relatioN form a partitioN of that set (i.e. aNy two are either equal or disjoiNt aNd every elemeNt of the set is iN some class). (1996-05-13)