20-CS-110-001 Introduction to Computer Science Fall 2010

Lies Like a Dog Puzzle

    The Kalotans are a tribe with a peculiar quirk: their males always tell the truth. Their females never make two consecutive true statements, or two consecutive untrue statements.

An anthropologist (let's call him Worf) has begun to study them. Worf does not yet know the Kalotan language. One day, he meets a Kalotan (heterosexual) couple and their child Kibi (also called "kid"). Worf asks the kid: ``Are you a boy?'' The kid answers in Kalotan, which of course Worf doesn't understand.

Worf turns to the parents (who know English) for explanation. One of them says: "Kibi said: `I am a boy.'" The other adds: "Kibi is a girl. Kibi lied."

Solve for the sex of the parents and Kibi.