Isaac, Richard E. (1995). The Pleasures of Probability. Springer. σελίδες 48–50. ISBN038794415X. Isaac generalizes this argument immediately to variable text and alphabet size; the common main conclusion is on p.50.
Marcus Tullius Cicero, De natura deorum, 2.37. Translation from Cicero's Tusculan Disputations; Also, Treatises On The Nature Of The Gods, And On The Commonwealth, C. D. Yonge, principal translator, New York, Harper & Brothers Publishers, Franklin Square. (1877). Downloadable text.