Barry Cipra is a freelance mathematics writer based in Northfield, Minnesota. He has been a contributing correspondent for Science magazine and a regular writer for SIAM News, the monthly newsletter of the Society for Industrial and Applied Mathematics. He wrote the first five volumes of What’s Happening in the Mathematical Sciences (American Mathematical Society, 1993-2002), and is the author of Misteaks... and How to Find Them Before the Teacher Does: A Calculus Supplement (A.K. Peters, Ltd., 2000). He received a Ph.D. in mathematics from the University of Maryland, College Park. E-mail: bcipra@rconnect.com