A valid arrangement of circles, with their
interiors shaded. Note that the straight
line is an infinite radius circle through $\infty$,
so it still counts.

David is a final year PhD student at UCL studying geometric group theory. When not doing maths he can usually be found singing or playing the flute.
More from Chalkdust
On the cover: Some assembly required
Trippy brain massages from Sam Palmer's artwork on the front of Issue 16My favourite LaTeX package
The Chalkdust editors share some of their favouritesIn conversation with Ulrike Tillmann
Sophie Maclean and David Sheard speak to a very top(olog)ical mathematician!Page 3 model: Solitons
SolitonsChalkdust issue 11 puzzle hunt #3
David Sheard sets the third puzzle. Can you solve it?On the cover: Apollonian packing
David Sheard explores the rich mathematics and history behind the Apollonian packing, and the cover of issue 11