In NBG set theory, classes are in some sense generalizations of sets. When dealing with sets, we view set functions as specific subsets of a Cartesian product. Is the definition the same for functions from one class to another?
I don't see any problem generalizing the notion of Cartesian products of sets to products of classes. I am only hesitant because after some googling, I have failed to find anything mentioning Cartesian products of classes.