On Start the Week Tom Sutcliffe finds out what goes on inside the mind of a mathematician. Cédric Villani explains the obsession and inspiration which led him to being awarded the Fields Medal, 'the mathematicians' Nobel Prize' in 2010. Zia Haider Rahman combines pure maths, investment banking and human rights in his exploration of how abstract theory can impact on real life. Vicky Neale reveals the beauty of prime numbers, while the director Morgan Matthews finds love in his film x+y at the International Mathematics Olympiad. Producer: Katy Hickman.