Burgess, John P. & Rosen, Gideon - A Subject With No Object: Strategies for Nominalistic Interpretation of Mathematics

Finally, after years of waiting, it is your turn to put a question to the Oracle of Philosophy. So you humbly approach and ask the question that has been consuming you for as long as you can remember: 'Tell me, O Oracle, what there is. What sorts of things exist?'

To this the Oracle responds: 'What? You want the whole list? Look, I haven't got all day. But I will tell you this: everything there is is concrete; nothing there is is abstract. Now go away and don't bother me.'