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Your reviewer takes me to task over my new book Why Beauty Is Truth (Books, May 25). Apparently my title is meaningless, my subtitle "A history of symmetry" is unhelpful, and "the cover image of a (non-symmetric) butterfly is hardly more revealing." Oh dear.

I can only assume that the reviewer failed to notice the jacket copy, with its mention of cubic equations, Galois, group theory and superstrings. As for the cover image, it is astonishingly symmetric for a living creature, right down to the scalloping of the wings and the major veins. Departures from symmetry are extremely tiny: the head is not quite aligned with the symmetry axis, and some areas of the wings are darker than their mirror images.

Having said that, the criticism is extraordinary for its complete irrelevance. The main function of a cover is to persuade potential readers to look inside the book. Ideally, it should also capture some aspect of the book. My butterfly is beautiful and invokes the idea of symmetry.

When a reviewer thinks it is worth devoting space to that kind of comment it is not surprising to find that most of the other criticisms are equally misdirected. For example, the chapter on Euclid was not dragged in to fill a supposed gap between Babylon and Omar Khayyam. A significant thread in my story is the geometric construction of regular polygons, and I needed to place Gauss's discovery about the 17-gon in its proper context, which is Euclid's construction of the equilateral triangle and the pentagon. Omar's use of conic sections to solve cubic equations rests on the work of Apollonius, who naturally joins Euclid in the appropriate chapter.

A few of the historical criticisms are more sensible, but even here the reviewer seems unable to distinguish between the kind of detailed discussion that belongs in a scholarly paper and the need to avoid cluttering a popular science book with pedantic fine points. The review misrepresents my book and is completely out of line with every other review that has been published.

Ian Stewart
Warwick University