Transcript Gremlins and Goblins

Gremlins and Goblins
• Gremlins always tell the truth. Goblins
sometimes lie. Unfortunately, their
appearance is identical.
• You are in a dungeon with two gremlins
and a goblin (but you don’t know which is
which). There is a red door and a blue
door. One door leads to the exit. The other
door leads to a pit of deadly venomous
snakes.
The Query
• Your objective is to find the exit. Your
companions give you some advice:
– Gorbnitz: The red door is the way out. I am
telling the truth!
– Grovnack: The blue door is the way out.
Gorbnitz is lying!!
– Glidnoph: I don’t know which door is the way
out, but Gorbnitz is telling the truth.
Solving the Problem
• Express the problem in first-order logic.
• Express the negated goal in first-order
logic and add it to the KB.
• Translate all of the knowledge into
standard form (clausal normal form).
• Apply resolution to derive a contradiction.
• The answer is in the bindings.
Describing the Problem
Describing the Negated Goal
Clausal Normal Form
Resolution Proof Tree
The Answer