1. Beall, J. C. (2009). Spandrels of truth. Oxford: Oxford University Press.
2. Blass, A. (2011). Are proper classes objects? http://mathoverflow.net/questions/71765/are-proper-classes-objects/71773#71773 . Accessed 1 Aug 2011.
3. Blass, A. (2013). The kunen inconsistency and definable classes. http://mathoverflow.net/questions/129498/the-kunen-inconsistency-and-definable-classes .
4. Boolos, G. (1984). To be is to be the value of a variable (or to be some values of some variables). The Journal of Philosophy, 81, 430–450.
5. Boolos, G. (1998a). Must we believe in set theory? In R. C. Jeffrey (Ed.), Logic, logic, and logic (pp. 120–132). Cambridge, MA: Harvard University Press.