ERNA at work

Abstract

Elementary Recursive Nonstandard Analysis, in short ERNA, is a constructive system of nonstandard analysis proposed around 1995 by Chuaqui, Suppes and Sommer. It has been shown to be consistent and, without standard part function or continuum, it allows major parts of analysis to be developed in an applicable form. We briefly discuss ERNA's foundations and use them to prove a supremum principle and provide a square root function, both up to infinitesimals. © 2007 Springer-Verlag Wien.