P. Bernays: 1964, On Platonism in Mathematics, reprinted in: P. Benacerraf and H. Putnam H. (eds): *Philosophy of Mathematics*, Prentice-Hall.

J. Brown: 1990, II in the Sky. In A.D. Irvine (ed): *Physicalism in Mathematics*. Kluwer Academic Publishers.

Cantor: 1932, *Gesammelte Abhandlungen mathematischen und philosophischen Inhalts*. Hrsg. E. Zermelo, Verlag von Julius Springer, Berlin 1932; reprinted: Springer-Verlag, 1980.

P.J. Cohen: 1971, Comments on the Foundations of Set Theory. In D. Scott (ed): *Axiomatic Set Theory*, Proceedings in Symposia in Pure Mathematics, 13, part 1, AMS, Provindence, Rhode Island.

H.B. Curry: 1951, *Formalist Philosophy ofMathematics*. North-Holland, Amsterdam.

K. Gödel: 1947, What is Cantor's Continum Problem?, reprinted in: P. Benacerraf and H. Putnam (eds): *Philosophy of Mathematics*, Prentice-Hall.

G.H. Hardy: 1929, Mathematical Proof. *Mind* 38: 1–25.

K. Kunen: 1980, *Set Theory*. North-Holland.

I. Lakatos: 1976, *Proofs and Refutations*. Cambridge University Press, Cambridge.

S. Mac Lane: 1986, *Mathematics: Form and Function*. Springer-Verlag.

Y. Moschovakis: 1980, *Descriptive Set Theory*. North-Holland.

J. PARIS and L. Harrington: 1977, A Mathematical Incompleteness in Peano Arithmetic. In J. Barwise (ed): *Handbook of Mathematical Logic*. North-Holland, Amsterdam.

A. Robinson: 1964, Formalism 64. In *Proceedings, International Congress for Logic, Methodology and Philosophy of Science*.

W.V.O. Quine: 1964, Two Dogmas of Empiricsm, reprinted in: P. Benacerraf and H. Putnam (eds): *Philosophy of Mathematics*. Prentice-Hall.

W.V.O. Quine: 1969, Existence and Quantification. In *Ontological Relativity and Other Essays*. Columbia University Press, New York.

S.G. Simpson: 1987, Subsystems of Z_{2} and Reverse Mathematics. In G. Takuti (ed.): *Proof Theory*. North-Holland, Amsterdam.

S.G. Simpson: 1988, Partial Realisations of Hilbert's Program.

*Journal of Symbolic Logic* 53: 349–363

CrossRef