Re: the unexpected hanging

From: Eliezer S. Yudkowsky (
Date: Sun May 13 2001 - 18:36:41 MDT

Lee Corbin wrote:
> Explaining exactly where and how the prisoner goes wrong
> isn't easy.

"Isn't easy" is, of course, relative to the explainer.

The prisoner can be fairly sure - say 99% sure - that the judge won't show
up on Friday, because even an idiot could see that wouldn't be a
surprise. But the prisoner can only be 80% sure that the judge won't show
up on Thursday, because it takes brains to realize that crossing off
Friday makes Thursday certain. If the judge hasn't shown up on Wednesday,
after all, the judge may just be the sort of really foolish person who
doesn't realize that showing up on Friday spoils the surprise, and may
hence fail to show up on Thursday. As for Wednesday; well, on Wednesday,
even if you're sure the judge won't show up on Friday, you're pretty
uncertain as to whether he'll show up on that day or Thursday. And on
Tuesday it's pretty much a complete surprise.

-- -- -- -- --
Eliezer S. Yudkowsky
Research Fellow, Singularity Institute for Artificial Intelligence

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