Hans Hermes – författare

This is a book about numbers - all kinds of numbers, from integers to p-adics, from rationals to octonions, from reals to infinitesimals. Who first used the standard notation for A? Why was Hamilton obsessed with quaternions? What was the prospect for "quaternionic analysis" in the 19th century? This is the story about one of the major threads of mathematics over thousands of years. It is a story that will give the reader both a glimpse of the mystery surrounding imaginary numbers in the 17th century and also a view of some major developments in the 20th.

This volume contains all of Frege's extant unpublished writings on philosophy and logic other than his correspondence, written at various stages of his career.

Das vorliegende, 1963 in erster Auflage erschienene Buch ist aus Vorlesungen hervorgegangen. Es soll eine Einführung in die klassische zweiwertige Prädikaten­ logik geben. Die Beschränkung auf die klassische Logik soll nicht besagen, daß diese Logik prinzipiell einen Vorzug vor anderen, nichtklassischen Logiken besitzt. Die klassische Logik empfiehlt sich jedoch als Einführung in die Logik wegen ihrer Einfachheit und als Fundament für die Anwendung deshalb, weil sie der klassischen Mathematik und damit den darauf aufgebauten exakten Wissenschaften zugrunde liegt. Das Buch wendet sich primär an Studierende der Mathematik, die in den An­ fängervorlesungen bereits einige grundlegende mathematische Begriffe, wie den Gruppenbegriff, kennengelernt haben. Der Leser soll dazu geführt werden, daß er die Vorteile einer Formalisierung einsieht. Der übergang von der Umgangssprache zu einer formalisierten Sprache, welcher erfahrungsgemäß gewisse Schwierigkeiten bereitet, wird eingehend besprochen und eingeübt. Die Analyse desmathemati­ schen Umgangs mit den grundlegenden mathematischen Strukturen führt in zwangloser Weise zum semantisch begründeten Folgerungsbegriff.

This book grew out of lectures. It is intended as an introduction to classical two-valued predicate logic. The restriction to classical logic is not meant to imply that this logic is intrinsically better than other, non-classical logics; however, classical logic is a good introduction to logic because of its simplicity, and a good basis for applications because it is the foundation of classical mathematics, and thus of the exact sciences which are based on it. The book is meant primarily for mathematics students who are already acquainted with some of the fundamental concepts of mathematics, such as that of a group. It should help the reader to see for himself the advantages of a formalisation. The step from the everyday language to a formalised language, which usually creates difficulties, is dis­ cussed and practised thoroughly. The analysis of the way in which basic mathematical structures are approached in mathematics leads in a natural way to the semantic notion of consequence. One of the substantial achievements of modern logic has been to show that the notion of consequence can be replaced by a provably equivalent notion of derivability which is defined by means of a calculus. Today we know of many calculi which have this property.

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.

Once we have accepted a precise replacement of the concept of algo­ rithm, it becomes possible to attempt the problem whether there exist well-defined collections of problems which cannot be handled by algo­ rithms, and if that is the case, to give concrete cases of this kind. Many such investigations were carried out during the last few decades. The undecidability of arithmetic and other mathematical theories was shown, further the unsolvability of the word problem of group theory. Many mathematicians consider these results and the theory on which they are based to be the most characteristic achievements of mathe­ matics in the first half of the twentieth century. If we grant the legitimacy of the suggested precise replacements of the concept of algorithm and related concepts, then we can say that the mathematicians have shown by strictly mathematical methods that there exist mathematical problems which cannot be dealt with by the methods of calculating mathematics. In view of the important role which mathematics plays today in our conception of the world this fact is of great philosophical interest. Post speaks of a natural law about the "limitations of the mathematicizing power of Homo Sapiens". Here we also find a starting point for the discussion of the question, what the actual creative activity of the mathematician consists in. In this book we shall give an introduction to the theory of algorithms.