Question 4
An island has 50 natives standing in a circle. Each announces first the age of the neighbour on the left, then the age of the neighbour on the right. A truth-teller gives both ages correctly; a liar decreases one age by 1 and increases the other by 1, choosing which. From all the announcements, can a visitor always determine the type of every native? (7 points)
Neutral editorial illustration.
Neutral editorial illustration.