“The surprising thing about this paper is that a man who could write it--would.”
Note quotation marks: Littlewood is repeating a joke without attribution. "Cross-purposes, Unconscious Assumptions, Howlers, Misprints, etc.", p. 59.
Littlewood's Miscellany (1986)
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John Edensor Littlewood 6
English Mathematician 1885–1977Related quotes
Introduction, p. vii.
On Writing Well (Fifth Edition, orig. pub. 1976)

Letter to Judy Stellings (18 November 1956), p. 30
1990s, The Proud Highway : The Fear and Loathing Letters Volume I (1997)

Luis Miguel Dominguin had undergone surgery after being wounded in a bullfight. From the context it is clear that his remark about Hemingway was a joke.
Source: The Dangerous Summer (1985), Ch. 10
“If cats could write history, their history would be mostly about cats.”