Category Vignettes

How to get rid of quantifiers?

Originating authors are Reinhard Oldenburg and Michele Artigue. How do computer packages do abstract algebraic problems such as proving statements “for all $x$” or finding whether a Real Number $x$ with certain conditions exists? Recent advances draw on theorems in…

The Revenge of the Infinitesimals

Originating author is Michèle Artigue. Infinitesimals played an essential role in the emergence and development of differential and integral calculus. The evident productivity of this calculus did not prevent recurrent and fierce debates about the nature of these objects and…

Classifying objects

Originating author is Christiane Rousseau. Mathematics offers tools for classifying objects. But is that of any practical use? More than we can imagine at first sight… It could allow us to conclude that a knot cannot be unknotted without cutting…

The Hairy Ball Theorem

Originating author is João Pimentel Nunes The Hairy Ball Theorem is from topology, that part of mathematics that is concerned with the form of spaces. For the most part, this result came from work at the end of the 19th…

Calculators, Power Series and Chebyshev Polynomials

Originating author is Graeme Cohen. Of all the familiar functions, such as trigonometric, exponential and logarithmic functions, surely the simplest to evaluate are polynomial functions. The purposes of this article are, first, to introduce the concept of a power series,…

Dimension

Von Christiane Rousseau Übersetzt aus dem Englischen von Eva Klein (Universität Würzburg) Wie misst man die Größe eines geometrischen Objekts? Für Teilmengen einer Ebene verwenden wir dazu oft Umfang, Länge, Flächeninhalt, Durchmesser, etc. Diese Maßbegriffe reichen jedoch nicht aus, um…

The shocking behaviour of moving fluids

Originating authors are David Mumford and Christiane Rousseau. Foreword: This vignette is more difficult than others. However, in a few pages, it tells you how to explain in simple terms one of the most difficult open problems at the beginning…

Public-key cryptography

Originating authors are Graeme L. Cohen (University of Technology, Sydney), Steven Galbraith (University of Auckland) and Edoardo Persichetti (University of Auckland). How can we safely send our credit card details over the internet, or using a mobile phone, when others…

SXEOLF NHB FUBSWRJUDSKB (PUBLIC KEY CRYPTOGRAPHY)

The need to create secure codes is said to go back to Julius Caesar, who moved letters in his messages up by three through the alphabet. That is encoding. How would you decode such a message? Modern day cryptography, which…