“Trees are approximately conical in shape . . . Cones are developable surfaces: they can be flattened out into a plane without being stretched or shrunk.” Photograph: Fabian Bimmer/AP
Consider a spherical Christmas tree

A minor seasonal challenge is how to distribute the fairy lights evenly around the tree, with no large gaps or local clusters. Since the lights are st(...)

Gauss’s work extended the theory of numbers in several directions, and its influence continued into the 20th century

You may never have heard of modular arithmetic, but you use it every day without the slightest difficulty. In this system, numbers wrap around when th(...)