7 In fairness to all concerned, this variability in readers’ mathematical backgrounds is a problem for pretty much anyone trying to write general-interest prose about math, a problem that Hardy refers to as “the restrictions under which I am writing. On the one hand my examples must be very simple, and intelligible to a reader who has no specialized mathematical knowledge…. And on the other hand my examples should be drawn from ‘pukka’ mathematics, the mathematics of the working professional mathematician.” Note that this sort of thing is a problem even for rather more “special-interest” writing like this book review itself. Is it, for example, necessary to inform or remind the average Science reader that Fermat’s Last Theorem (c. 1637) states that where n is an integer and n > 2, the equation x ⁿ + y ⁿ = z ⁿ has no nonzero integer solutions? or that Goldbach’s Conjecture (or rather the “strong” G.C. as reformulated by Leonhard Euler in 1742) is that every even integer > 4 can be expressed as the sum of two prime numbers, etc.? As it happens, this reviewer is not certain whether it’s necessary or not, and the fact that these lines have not been deleted by Science’s editors (i.e., that you are reading them at all) may indicate that the editors are not totally sure either.