Pierre Berloquin, whose book is illustrated by Jean Gourmelin, explains: ‘André Balland introduced us. He wished to publish my Souvenir d’enfance d’Évariste Gallois (Évariste Gallois’ Childhood Memory). Although he found it too short, he was looking for a suitable theme to publish a new collection of Gourmelin’s drawings. Fleshing out my text with his illustrations was an excellent idea. The chiselled mischievousness of his drawings went well with my unconventional thoughts on logic and the psychology of mathematics. From the start, we agreed there would be three kinds of illustrations: some he already possessed which matched the topic, some suggested to him after reading the text, and others I would imagine, and he would draw on my instructions.’