## Articles

*Plus*, Marcus du Sautoy continues his exploration of the greatest unsolved problem of mathematics: The

**Riemann Hypothesis**.

**paper folding**.

**Riemann Hypothesis**. In the first part, we find out how the German mathematician Gauss, aged only 15, discovered the dice that Nature used to chose the primes.

**Calculus**is a collection of tools, such as differentiation and integration, for solving problems in mathematics which involve "rates of change" and "areas". In the first of two articles aimed specially at students meeting calculus for the first time, Chris Sangwin tells us about these tools - without doubt, the some of the most important in all of mathematics.

*Plus*takes an illustrated tour of an extraordinary geometric construction: the

**Klein bottle**.

**number 23**.

**data compression**.

**Isaac Newton**and David Gregory - took place on the campus of Cambridge University. The discussion concerned the

**kissing problem**, but it was to be another 260 years before the problem was finally solved.