What is the name of the logical puzzle, where one always lies and another always tells the truth? So i was solving exercises in propositional logic lately and stumbled upon a puzzle, that goes like this:

Each inhabitant of a remote village always tells the truth or always lies. A villager will only give a "Yes" or a "No" response to a question a tourist asks. Suppose you are a tourist visiting this area and come to a fork in the road. 
  One branch leads to the ruins you want to visit; the other branch leads deep into the jungle. A villager is standing at the fork in the road. What one question can you ask the villager to determine which branch to take? 

I intuitively guessed the answer is "If I asked you this path leads to the ruins, would you say yes?". So my questions are:


*

*What is the name and/or source of this logical riddle?

*How can i corroborate my answer with mathematical rigor?


Knights and Knaves?
How: read about it.
