Half a year ago I read Knuth’s book Surreal Numbers. Written in the style of a children’s book it explains a new way of doing mathematics using sets, but more generally explores the process of discovering such a method. Knowing Knuth’s ruthless attention to detail and seeing some things that appeared to be errors, I sent an email to him explaining the issues.
I was surprised and excited to receive a handwritten response from Knuth:
Knuth’s responses are written in mechanical pencil and I couldn’t get them to scan clearly so here’s a transcription:
- “Not true; you don’t understand the empty set. See Martin Gardner, Mathematical Magic Shop, chapter 1.”
- “? They are not on a desert island, they are in Yemen.”
- “Live and learn, I guess.”
- “Glad to hear it”
end. “Thanks for reading as far as page 110 in spite of perceived errors
Best wishes don knuth”
Some of his responses seem quite dodgy. I didn’t describe the context for the errors, perhaps he’d forgotten some of the details of the book so they didn’t make much sense. Or maybe he didn’t want to correct minor errors in it anymore. (Both of which seem rather likely.) Anyway, it’s still cool to receive a letter from such a great scholar.