Three people are being interviewed for a logic professor position. There is one final test.
They are blindfolded and told either a black or a white dot will be applied to their foreheads. All three are then given a black dot. They are then sat in a circle. When the blindfold is removed they are asked to raise their hand if they see a black dot on either of the other two applicants' foreheads. (all three raise their hands).
They are then told that the first person to identify what color dot is on his own forehead and how he knows it gets the job.