1. Beth, E. W. (1970). Aspects of modern logic. D. Reidel Publishing Company.
2. Husserl, E. (2003) Philosophy of arithmetic. psychological and logical investigations—with supplementary texts from 1887–1901. Edmund Husserl collected works (Vol. X). Kluwer Academic Publishers. Translated by Dallas Willard.
3. Wikipedia Contributors. (2023). Ultrafinitism. In Wikipedia, the free encyclopedia. Retrieved 20:14, August 24, 2023, from https://en.wikipedia.org/w/index.php?title=Ultrafinitism&oldid=1148928207.