Olsson explores the work of both Weils, hoping to understand their shared commitment to truth. Simone – whom TS Eliot described as “a kind of genius akin to that of a saint” – was devoted to a religious ideal of the good. In Olsson’s formulation, she used maths as something like a meditative practice, allowing it to “surpass the part of brain that does math”... Olsson has taken on a complicated mix of subjects. The book is part memoir, part biography and part a general history of 20th-century maths. Its method is aphoristic and digressive: short sections are juxtaposed, sometimes with a kind of cumulative energy and sometimes more randomly. There were times when I longed for something more expansive, for the characters to break out of their small sections. Also I wanted to hear more about the Weils and less (or more intimately) about Olsson, whose own experiences as detailed here are rather less profound than those of her subjects. But this ordinariness does have the advantage of making her an everywoman guide, and what she does brilliantly is to explain the maths clearly and often fascinatingly. Also, and this must be unique among accounts of the Weils, she creates a vivid sense of Simone grappling with the maths alongside us.