On March 22, 1977, as I was drafting Section 7.1 of The Art of Computer Programming, I read four papers by Peter van Emde Boas that turned out to be more appropriate for Chapter 8 than Chapter 7. I wrote a five-page memo entitled "Notes on the van Emde Boas construction of priority dequeues: An instructive use of recursion,'' and sent it to Peter on March 29 (with copies also to Bob Tarjan and John Hopcroft). The final sentence was this: "Beware of bugs in the above code; I have only proved it correct, not tried it.''
-- from the homepage of Donald Knuth