Donald Knuth, the renowned computer scientist, has long offered rewards for errors found in his books—a practice that has become folklore in computer science. According to Thomas Huehn, who documented his experience on his personal website, he received one of these coveted checks after finding an error in Knuth’s “Computer Modern Typefaces.”
The error Huehn discovered was particularly notable for its location: on page one, in the first paragraph, in the very first word of the book. Despite having found what he believed was a legitimate error, Huehn did not report it immediately. Instead, he waited and rechecked his finding for months to avoid making a mistake himself. He even consulted a local university expert, though that person initially dismissed his excitement about the discovery.
Huehn notes that finding any error in Knuth’s books is remarkable given the scale of scrutiny they receive. “His books have been combed through by thousands and thousands of people,” Huehn wrote, adding that he considered it improbable he could find something missed by more experienced readers.
“Computer Modern Typefaces” is part of Knuth’s “Computers & Typesetting” series, where it serves as Volume E—a less frequently read work compared to Knuth’s other major publications like “The TeXbook” or “The Art of Computer Programming.” Despite being less widely read, Huehn notes that most people who have engaged with the book would likely have encountered the error he found.
Knuth’s practice of rewarding error-finders with checks has evolved over time. According to Huehn, Knuth has not been issuing real checks for many years. Instead, the reward now comes in the form of fantasy certificates from a fictional entity: the Bank of San Serriffe.
Huehn’s check displays “0x$1.20” (equivalent to decimal $2.88) as the reward amount. Years after his initial discovery, Huehn submitted another proposed error, but Knuth determined it was not actually an error. However, Knuth provided a detailed explanation of why Huehn was mistaken and awarded an additional check for $0.32, crediting a suggestion embedded in Huehn’s bug report as valuable enough to warrant the reward.
Key facts
- Donald Knuth awards checks to readers who find errors in his books, including typographical errors
- Thomas Huehn found an error on page one of ‘Computer Modern Typefaces,’ the first word in the first paragraph
- Huehn verified his finding over several months before submitting it to avoid making a mistake
- Knuth has replaced real checks with fantasy certificates from the Bank of San Serriffe in recent years
- Huehn received multiple checks: one for the initial error and another for a suggestion in a later submission