Two lines in a plane always intersect in a single point ... *unless* the lines are parallel. This annoying exception is constantly inserting itself into otherwise simple mathematical statements. **Burkard Polster** and **Marty Ross** explain how to get around the problem.

In the first of a new series 'Imaging Maths', *Plus* takes an illustrated tour of an extraordinary geometric construction: the **Klein bottle**.

Imagine stepping inside your favourite painting, walking around the light-filled music room of Vermeer's "The Music Lesson" or exploring the chapel in the "Trinity" painted by Masaccio in the 15th century. Using the **mathematics of perspective**, researchers are now able to produce three-dimensional reconstructions of the scenes depicted in these works.