These corps may themselves be divided into ranks ("grades", called "classes" in certain corps). For instance, the corps of university professors is a category A corps divided into 3 classes: second class (equivalent to an American associate professor), first class (full professor), exceptional class (leading full professor in his area). Generally, to avoid rank inflation, the number of civil servants in the higher ranks (especially "exceptional class") is constrained by a maximal percentage of the total number of civil servants of the corps.