Bernard Bolzano’s paper Rein analytischer Beweis des Lehrsatzes, dass zwischen jezwei Werthen, die ein entgegengesetztes Resultat gewähren, wenigstens eine reelleWurzel der Gleichung liege was published in 1817. It presents a ”purely analytic proof” of the intermediate value theorem for the polynomials of variable x. Aside from polynomials, Bolzano considers other kinds of functions, however the domain of these functions is not clearly defined. In this article, we show that the variable x ranges over real numbers. Specifically, we identify the axioms for the ordered field that Bolzano implicitly applies. We also identify the versions of continuity axiom, and show that while some of them are implicitly applied, others are explicitly stated as ”basics truths”.
PL
Bernard Bolzano’s paper Rein analytischer Beweis des Lehrsatzes, dass zwischen je zwei Werthen, die ein entgegengesetztes Resultat gewähren, wenigstens eine reelle Wurzel der Gleichung liege was published in 1817. It presents a ”purely analytic proof” of the intermediate value theorem for the polynomials of variable x. Aside from polynomials, Bolzano considers other kinds of functions, however the domain of these functions is not clearly defined. In this article, we show that the variable x ranges over real numbers. Specifically, we identify the axioms for the ordered field that Bolzano implicitly applies. We also identify the versions of continuity axiom, and show that while some of them are implicitly applied, others are explicitly stated as ”basics truths”.
In his 1887's Mitteilungen zur Lehre von Transfiniten, Cantor seeks to prove inconsistency of infinitesimals. We provide a detailed analysis of his argument from both historical and mathematical perspective. We show that while his historical analysis are questionable, the mathematical part of the argument is false.