Alexander Prestel

Positivity is one of the most basic mathematical concepts. In many areas of mathematics (like analysis, real algebraic geometry, functional analysis, etc.) it shows up as positivity of a polynomial on a certain subset of R^n which itself is often given by polynomial inequalities. The main objective of the book is to give useful characterizations of such polynomials. It takes as starting point Hilbert's 17th Problem from 1900 and explains how E. Artin's solution of that problem eventually led to the development of real algebra towards the end of the 20th century. Beyond basic knowledge in algebra, only valuation theory as explained in the appendix is needed. Thus the monograph can also serve as the basis for a 2-semester course in real algebra.

Mathematical Logic and Model Theory: A Brief Introduction offers a streamlined yet easy-to-read introduction to mathematical logic and basic model theory. It presents, in a self-contained manner, the essential aspects of model theory needed to understand model theoretic algebra. As a profound application of model theory in algebra, the last part of this book develops a complete proof of Ax and Kochen's work on Artin's conjecture about Diophantine properties of p-adic number fields. The character of model theoretic constructions and results differ quite significantly from that commonly found in algebra, by the treatment of formulae as mathematical objects. It is therefore indispensable to first become familiar with the problems and methods of mathematical logic. Therefore, the text is divided into three parts: an introduction into mathematical logic (Chapter 1), model theory (Chapters 2 and 3), and the model theoretic treatment of several algebraic theories (Chapter 4). This book will be of interest to both advanced undergraduate and graduate students studying model theory and its applications to algebra. It may also be used for self-study.

Absolute values and their completions -like the p-adic number fields- play an important role in number theory. Krull's generalization of absolute values to valuations made applications in other branches of mathematics, such as algebraic geometry, possible. In valuation theory, the notion of a completion has to be replaced by that of the so-called Henselization. In this book, the theory of valuations as well as of Henselizations is developed. The presentation is based on the knowledge acquired in a standard graduate course in algebra. The last chapter presents three applications of the general theory -for instance to Artin's Conjecture on the p-adic number fields- that could not be obtained by the use of absolute values alone.

Absolute values and their completions -like the p-adic number fields- play an important role in number theory. Krull's generalization of absolute values to valuations made applications in other branches of mathematics, such as algebraic geometry, possible. In valuation theory, the notion of a completion has to be replaced by that of the so-called Henselization. In this book, the theory of valuations as well as of Henselizations is developed. The presentation is based on the knowledge acquired in a standard graduate course in algebra. The last chapter presents three applications of the general theory -for instance to Artin's Conjecture on the p-adic number fields- that could not be obtained by the use of absolute values alone.

Positivity is one of the most basic mathematical concepts. In many areas of mathematics (like analysis, real algebraic geometry, functional analysis, etc.) it shows up as positivity of a polynomial on a certain subset of R^n which itself is often given by polynomial inequalities. The main objective of the book is to give useful characterizations of such polynomials. It takes as starting point Hilbert's 17th Problem from 1900 and explains how E. Artin's solution of that problem eventually led to the development of real algebra towards the end of the 20th century. Beyond basic knowledge in algebra, only valuation theory as explained in the appendix is needed. Thus the monograph can also serve as the basis for a 2-semester course in real algebra.

Die Schwierigkeit Mathematik zu lernen und zu lehren ist jedem bekannt, der einmal mit diesem Fach in Berührung gekommen ist. Begriffe wie "reelle oder komplexe Zahlen, Pi" sind zwar jedem geläufig, aber nur wenige wissen, was sich wirklich dahinter verbirgt. Die Autoren dieses Bandes geben jedem, der mehr wissen will als nur die Hülle der Begriffe, eine meisterhafte Einführung in die Magie der Mathematik und schlagen einzigartige Brücken für Studenten.Die Rezensenten der ersten beiden Auflagen überschlugen sich.

A book about numbers sounds rather dull. This one is not. Instead it is a lively story about one thread of mathematics-the concept of "number"­ told by eight authors and organized into a historical narrative that leads the reader from ancient Egypt to the late twentieth century. It is a story that begins with some of the simplest ideas of mathematics and ends with some of the most complex. It is a story that mathematicians, both amateur and professional, ought to know. Why write about numbers? Mathematicians have always found it diffi­ cult to develop broad perspective about their subject. While we each view our specialty as having roots in the past, and sometimes having connec­ tions to other specialties in the present, we seldom see the panorama of mathematical development over thousands of years. Numbers attempts to give that broad perspective, from hieroglyphs to K-theory, from Dedekind cuts to nonstandard analysis.

Ein wesentliches Ziel dieses Buches ist, Studenten des Hauptstudiums und interessierten Mathematikern die Möglichkeit zu eröffnen, die bekanntesten, in der Algebra zur Zeit üblichen modelltheoretischen Schlüsse kennen und verstehen zu lernen. Die Modelltheorie beschäftigt sich primär mit der Untersuchung der Modelle von Axiomensystemen, die in der Sprache der Logik erster Stufe formuliert sind. Die meisten, der in der Mathematik üblichen Axiomensystemen, gehören dazu.

Das vorliegende Blichlein ist aus Vorlesungen hervorgegangen, die wir abwechselnd an der Universitat Konstanz hielten und noch immer halten. Die Absicht dieser Vor- lesung ist es, Mathematikstudenten mittlerer Semester einen Einblick in die Mengen- lehre zu vermitteln, der ihnen gleichzeitig die flir die Mathematik wichtigsten mengen- theoretischen Begriffe und Satze an die Hand gibt. Diese Vorlesung halten wir gewohnlich zweistlindig im Sommersemester. Hieraus resultiert die Anzahl der Kapitel - jede Woche wird ein Kapitel besprochen. Wir setzen dabei eine gewisse Vertrautheit des Studenten im naiven Umgang mit Mengen aus den ersten Semestern voraus. Auch flihren wir bei Anwendungen der Mengenlehre nicht aile Beweise detailliert aus, sondern begnligen uns oft mit der Angabe der wich- tigsten Schritte. Dies gilt zum Beispiel flir den Autbau des Zahlsystems, speziell flir die Kapitel4 und 5. Urn in Kapitel 10 neben einfachen Anwendungen des Auswahl- axioms auch tieferliegende bringen zu konnen, sind wirt dort gezwungen, Vertraut- heit mit den Begriffen und Satzen der jeweiligen Theorie vorauszusetzen. Grundsatz- lich lassen sich jedoch aile in Beweisen bestehenden Lucken routinemall>ig schliell>en. Der von uns gewahlte Zugang zur Mengenlehre ist axiomatisch, vermeidet jedoch moglichst eine zu formale Darstellung. Wir versuchen, der mathematischen Praxis so nahe wie moglich zu bleiben, ohne dadurch allerdings eine mOgliche Formalisierbar- keit aus den Augen zu verlieren. Dber die Durchflihrung einer solchen Formalisierung (nach von Neumann, Godel, Bernays) berichten wir im Epilog.