You are a spy in a hostile country, trying to escape the local authorities. As a disguise, you join the local Knavy, which is like a navy, but is made up entirely of knaves (people who alternate telling the truth and lying). You get word that a ship, the HMS Levik is docked in the harbor to help you escape. The problem is, there are five ships in port (at docks one through five) and none of them are marked with a name.
  You manage to talk with two old sea captains in the Knavy about which ship is which. They talk some, but you don't know if their first statement is a truth or a falsehood.
  Based on their curious descriptions, can you figure out which ship is the HMS Levik?

CAPT. HUDSON:
1. The Salamander is not moored next to the Revenge.
2. The Antimony is moored at dock one.
3. The Levik is moored at dock two.
4. The Defiance is moored next to the Levik

CAPT. BAFFIN
1. The Defiance is not moored at dock two.
2. The Levik is moored at dock four.
3. The Salamander is moored next to the Revenge.
4. The Antimony is not moored next to the Salamander.

(In reply to Solution by Shaun)

The "assume" part doesnt sound like a proof. I'd rather reason that:

the 1st statement by Hudwon is opposite the 3ird statement by Baffin - if one is true, the other is false - so the 1st statement by Hudson is also opposite the 1st statement by Baffin, and odd statements from one captain are the same (both true or both false) as even statements from the other captain.

the 3rd statement by Hudson and the 2nd statement by Baffin may not both be true, but they must be the same (as we saw before) so they have to be both false and thus, without assuming anything, it follows that Hudson lied first and Baffin told the truth first.

Posted by Oskar on 2004-05-27 08:12:20