1. Shapiro, S. (1991). Foundations Without Foundationalism: A Case for Second-Order Logic. Oxford: Clarendon Press, New York.
2. Frege, G. (1884). Die Grundlagen der Arithmetik: Eine logisch mathematische Untersuchung über den Begriff der Zahl. W. Koebner, Breslau. English translation by J. L. Austin.
3. Frege, G. (1893). Grundgesetze der Arithmetik vol. 1. H. Pohle, Jena. English translation by P. Ebert and M. Rossberg.
4. Dedekind, R. (1888). Was sind und was sollen die Zahlen? Braunschweig: Vieweg.
5. Boolos, G. (1987). The consistency of Frege’s Foundations of Arithmetic. In J. J. Thomson (Ed.), On Being and Saying: Essays in Honor of Richard Cartwright (pp. 3–20). MIT Press, Cambridge, MA. Reprinted in Logic, Logic, and Logic, pp. 183–201, by G. Boolos, 1999, Harvard University Press.