My mother has written a biography of my brother Alan. It was certainly a tour de force on her part to write it, as she did, in her seventies. It has rightly been praised, by others better qualified to judge than I am, as a revealing study of a son who became, undoubtedly, a mathematical genius.

I start off, therefore, at a disadvantage. Much of the ground has already been covered, and certainly, so far as Alan's childhood is concerned, far better and in more detail than I could have done it myself. But it is sufficiently obvious to any discerning reader of that book that a false note has been struck somewhere: could Alan have been quite that paragon of virtue that my mother describes? Yet, if an elder brother ventures to suggest the contrary, it can easily be suggested that he is jealous and sour. This is a risk I must accept. My only concern is to put the record straight, however hazardous the enterprise.

My brother Alan was born on 21 June 1912 in a London nursing home. For me, it was a halcyon time, for my father, perforce, had to look after me for the one and only time in his life. His solution of the problem could not have been bettered: we visited the White City, went on roundabouts, ate in restaurants and travelled around the metropolis on the tops of buses with the tickets stuck in our hat-bands.