Excuse me if I'm being too strict here but there seems to be a glaring gap in the definition of what a PRC(squared) class is on p42 of the textbook.
The definition states that
1) the initial functions must belong to the class,
2) a function obtained from functions belonging to the class (by either composition or recursion) also belongs to the class
From experience in previous modules, it seems that the definition is missing a 3rd point:
3) Only the functions which qualify through 1) and 2) belong the the class.
Without point 3), any other function I choose could also be included in the class, since points 1) and 2) have already been fulfilled.