This is a really fun discussion between two absolutely brilliant philosophers.  Craig knows less mathematics but more philosophy than Oppy, yet he holds his own quite well on the math.  The same in reverse can be said of Oppy.  Speaking for myself, I know the math better and the philosophy less, but I find both men to be honest to both subjects.  I find Craig’s arguments to be quite compelling, and Oppy’s responses to be pretty much ad hoc.  He is trying to dismiss the argument, but every new attack on the argument is met by an even more convincing response.  Bottom line, Oppy has no explanation for the usefulness of mathematics.  All he can really do is say that it is not quite as useful as Craig is saying, but this rings hollow.  Oppy tries to create the impression that there are other explanations, but he does not present his own explanations of the usefulness of math.

Of course, this is the response of a believer, so it may be biased, so take what I say for what it is worth.  Thanks for turning me on to this discussion.  I really loved the friendly and respectful attitude of all three in the discussion.  We need more of this sort of thing.