|Covid-19|Hrbacek, Karel; Jech, Thomas. Introduction to set theory. Third edition. Monographs and Textbooks in Pure and Applied Mathematics, 220. Marcel Dekker, Inc., New York, 1999. xii+291 pp. ISBN 0-8247-7915-0
Hrbáček, Karel. Axiomatic foundations for nonstandard analysis. Fund. Math. 98 (1978), no. 1, 1–19.
Ballard, David; Hrbáček, Karel. Standard foundations for nonstandard analysis. J. Symbolic Logic 57 (1992), no. 2, 741–748.
Hrbacek, Karel. Nonstandard set theory. Amer. Math. Monthly 86 (1979), no. 8, 659–677.
Karel Hrbáček Wikipedia
Karel Hrbáček (born 1944) is professor emeritus of mathematics at City College of New York. He specializes in mathematical logic, set theory, and non-standard analysis.