One day you meet three persons, each either a Knight or a Liar. You ask "How many of you are knights?", and the first person answers "Grok!".
Not understanding, you ask the second one "What does 'Grok' mean?", and he answers "One", but then the third one cries out "That's false!".
What can you tell about each person, if anything?
A is Knight, B is Liar and C is Knight.
B can't be Knight: that would mean C to be a Liar and that would tell that A was speaking truth. There would be two knights so that would be incoherent with grock meaning "one".
So, if B is a Liar, than C must be a Knight. Also, the total number of knights has to be two, so A is the other Knight.
Posted by vj
on 2007-06-29 09:52:39