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Know yourself (Posted on 2007-07-06) Difficulty: 1 of 5
At the Knights and Liars island, a logician wanted a sure fire method to know whether a native was a Knight or a Liar, but met with some problems.

First, he rashly tried simply asking "Are you a Knight?" or "Are you a Liar?", but he soon realized that this would never work. Also, there were some natives who didn't even know what they were!

Then, being logic-oriented, he started with complex combinations like "What would you answer if I asked you...?" but most persons lost interest and didn't even try to work out an answer.

Then, he changed to a simpler "Is this shirt red?" pointing at his own clothes, but that failed when he met a daltonic person.

A simple "Are you talking to me?" also failed; most thought the answer was "No" since they had been no conversation; the logician just popped up and asked his question.

Arithmetic was no good either: most natives had no use for it, and couldn't even calculate 1+1. (And they also couldn't read, by the way.)

At last, he came upon a question that could never be answered "YES" by a Knight, or "NO" by a Liar.

What simple question (up to three words is "simple"; four or more starts getting complex) could he ask?

Can you also think of some other seemingly good questions, and how they could fail?

No Solution Yet Submitted by Federico Kereki    
Rating: 4.0000 (2 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Salution V2 | Comment 9 of 12 |

It can not be "do knights lie?" because "lie" has different meanings.  Being knights, they surely lie in ambush, or lie in bed at night.

"Are you dead?" is a much cleaner (gramatically, this is logic, not philosophy :) ) question where there can be no aambiguous response.


  Posted by Tyryt on 2007-08-14 14:31:19
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