[Superjedi]: The question one could ask is, "If I were to ask your brother whether you always tell the truth, what would he say?" A reply of "no" means you are talking to the truth teller, a reply of "yes" means you are talking to the liar.
Another possible question is, "If I were to ask you whether you always tell the truth, what would you say?" In this case a reply of "yes" means you are talking to the truth teller and a reply of "no" means you are talking to the liar.
Both questions take advantage of the liar lying about what he or his brother would say, creating a double negative type situation.
[Superjedi]: but.. replace guard with brother..
To [Superjedi]: Doesnt get you the answer to the correct Doorway
To [Superjedi]: So you know which one lies & which tells the truth BUT u still dont know heaven from hell
[Superjedi]: You could ask the person that "What would the other community person answer if I ask him the road to heaven". Whatever the answer or the road he points to, take the other road.
Case 1: If you meet someone who always speak truth would say that the other community guy would lie and should you the wrong road.
Case 2: If you meet someone who always lie would lie that the road to heaven is xxx.
So, in either case, the road which the person would show is the wrong road, so take the other road.
This was answered by one of my friend while I was studying Computer in Pune, India.
To [Superjedi]: Ok you know how to Surf
[Superjedi]:
[Superjedi]: that is what i do all day long
[Superjedi]: didnt want to post it on forums to give others a chance