This logic puzzle has been declared the most difficult puzzle in the world. It was invented several decades ago. The puzzle is called “Green Eyed Dragons”. It has great popularity all over the world. At Harvard University, this puzzle is given to physics students in the form of a kind of additional task.
The puzzle occurs in several different forms with more or less clues that bring a solution. Logic is needed for the solution.
The most difficult puzzle in the world: “Green Eyed Dragons”
You have arrived to visit a remote and deserted island inhabited by 100 very friendly dragons. All the inhabitants of the island (dragons) have green eyes. Dragons have not seen a human being for centuries. They are very excited about your visit so they take you around the island and show you the life of dragons. Dragons seem quite normal. You soon learn something very unusual. There is a rule on the island that if a dragon ever finds out he has green eyes, he will have to give up all his dragon powers at exactly midnight and turn into a long-tailed swallow.
There are no mirrors on the island. Dragons never talk to each other about eye color and live in blissful ignorance for hundreds of years. When you were ready to leave, all the dragons gathered to greet you. You thanked them with many tears for the hospitality. After that, you decided to tell them something that dragons already know (every dragon sees the color of the eyes of other dragons). You tell all the dragons that at least one of them has green eyes. Of course you didn’t mean the consequences. You left the island and went on your way.
The riddle reads: What would happen next assuming that dragons are unmistakably logical beings.
The solution to the puzzle: you can find the solution on the Internet or come up with a solution yourself and then search the Internet for the correctness of your solution. This is not a play on words or a trick question. In the puzzle, some data is key to the final solution. The solution is logic.