There was a second thread to his story, that of the English schoolmaster's friendship with the German boy which remained 'suspended in an atmosphere of semi-Platonic sentimentality'.
This for Joan represented a quality of self-restraint that deserved admiration, but Alan, who had often teased Fred in terms rather like these, would probably have taken a different view.
The book was saved from the obvious danger, one that Evelyn Waugh had mocked in Put Out More Flags, by the stringency and sophistication with which it examined the contradictions.
The personal realities were ever questioning, and questioned by, a political background which included the late-1930s Nazi propaganda about boy-corrupting Jews and Catholic clergy.
On this level it served Alan as a way of saying that of his 'tendencies' could not be separated from his place in society, nor regarded as peripheral to his own freedom and consistency of mind.
Although he had dropped away from the direct cryptanalytic work, Alan remained within the Bletchley fold, and was to be seen in the cafeteria off duty.
Conversation at these times often revolved round mathematical and logical puzzles,
and Alan was particularly good at taking some quite elementary problem and showing how some point of principle lay behind it—or conversely, illustrating some mathematical argument with an everyday application.
It was part of his special concern for connecting the abstract and the concrete, as well as a pleasure in demystifying the higher mathematician's preserve.
It might be wallpaper patterns for an argument about symmetries.
His 'paper tape' in Computable Numbers had the same flavour, bringing an 'abstruse branch of logic' down to earth with a bump.