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My Knuth reward check (arcfn.com)
99 points by chrismealy 1970 days ago | hide | past | web | 23 comments | favorite

Wow, I was not expecting this article of mine to appear on Hacker News. The error I found was in volume 4a page 574 (as the memo line on the check shows). The solution to exercise 67 on that page says a particular circuit uses 6 ANDN gates, which I thought should be NAND gates. It gets a bit more complicated because Knuth was referring to the ANDN op code for MMIX, but there was still a mistake. (The other error I noticed was n choose k on page 824, but I checked the errata and it had already been found.)

well, what was the mistake then?

To save anyone else the trouble: the errata can be found at http://www-cs-faculty.stanford.edu/~uno/taocp.html , but it hasn't been updated to include this.

I have to admit that trying to find an error in a book is a strange vacation goal

Come on, I can only wish I was smart enough to set myself such a goal realistically. And to reach it? Would make this a vacation of a lifetime.

Found two errors back around 2000 or 2001. Cashed both checks. Figure he would want to keep the balance correct on his accounts. :) Only slightly regret it.

So it's a fake check?

Knuth stopped writing real checks due to the possibility of check fraud: http://www-cs-faculty.stanford.edu/~knuth/news08.html.

For that matter, almost all recipients considered the bragging values of the checks to be worth more than the few dollars in reward money; very few (or none) have been cashed.

I didn't realize that he's sending printed checks from his fictional bank. That's better than the old checks--I love the "0x$" and "hexadecimal dollars".

I cashed mine, but photocopied it first.

Still seems like a bit of a gyp. I hope that Knuth is willing to provide a real cheque for real money if you ask. He did, after all, promise real money.

From the linked page in your parent: "It turns out that only 9 of the first 275 checks that I've sent out since the beginning of 2006 have actually been cashed. The others have apparently been cached. So this change in policy will probably not affect too many people. On the other hand, I don't like to renege on promises, so I shall do my best to find a suitable way to send money to anyone who really prefers legal tender."

I'm sure you can sell that for more than $2.56. Hell, if you get one I'll commit to buy it off you for $5 plus postage. Email in profile.

Why would you want a DK check with someone else's name on it?

somethings you just gotta earn yourself.

it is a fake check, but it is from Knuth. account balances are on his bank website: http://www-cs-faculty.stanford.edu/~knuth/boss.html

I assume the error wasn't included to save Mr. Knuth from an avalanche of people "finding" the same error and demanding a check.

That's not the way it works; the "finder's fee" goes only to the first person to find an error.

Knuth also pays for suggested improvements, but these are a bit harder to get.

(Not that you asked, but I've got one of each.)

Cool. Thanks for the clarification.

This will get downvoted but...

Until we actually know what the error was, it's not true.

What are you trying to say? That the author may be lying? He would be found out soon enough - it would be stupid to try. That the error is not real? Knuth seems to think so, and the author is primarily claiming to have received a check anyway.

It would be reasonable to reveal the error in question, rather than tease us with just the cheque. Besides, Knuth or not, it's still valid when we learn what it is.

In case you hadn't noticed: http://news.ycombinator.com/item?id=2525309.

Well then, -10 karma, it was worth it :)

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