## Articles

**Alison Boyle**investigates aperiodic tilings, which have had unexpected applications in describing new crystal structures.

**Bill Casselman**writes about the intriguing amateur mathematician Henry Perigal, who took his elegant proof of Pythagoras' Theorem literally to his grave - by having it carved on his tombstone.

**Imre Leader**looks at the colourful world of Ramsey Theory.

**Tim Gent**explains.

**John Dickson**explains what derivatives are, and how they can be both risky, and used to reduce risk.

Emmy Noether, pioneering female mathematician, died 80 years ago.

**John Webb**takes us through some of the mathematics involved, introducing us to some of the colourful characters who led the way.