Let the relation R on set A be reflexive, then it is called a compatible relation. Let r be a compatible relation on set a, if c? A. If any two elements in C, A 1 and a2, have a 1Ra2, then C is said to be a compatible class generated by the compatibility relation R. Let R be a compatible relation on the set A, and a compatible class that cannot really be included in any other compatible class is called the maximum compatible class, and it is recorded as CR.