1. Adamowicz, Z., and P. Zbierski, Logic of Mathematics: A Modern Course of Classical Logic, Wiley, New York 1997.
2. Avigad, J., and R. Zach, The epsilon calculus, in E. N. Zalta (ed.), The Stanford Encyclopedia of Philosophy (Summer 2016 Edition).
https://plato.stanford.edu/archives/sum2016/entries/epsilon-calculus/
3. Bigelow, J., The Reality of Numbers, Oxford University Press, Oxford 1988.
4. Church, A., Introduction to Mathematical Logic (Vol. I), Princeton University Press, Princeton NJ 1956.
5. Corcoran, J., Schemata: the concept of schema in the history of logic, Bulletin of Symbolic Logic 12:219–240, 2006.