https://www.physics.harvard.edu/uploads/files/undergrad/probweek/prob2.pdf https://www.physics.harvard.edu/uploads/files/undergrad/probweek/sol2.pdf the solution is clear until this point: The point is that it is only after you make your announcement that the chain is extended the final step to the Nth dragon. The fact that the Nth dragon heard your statement is critical to the truth of this complete chain. So, in the end, it turns out to be of great importance how far the chain, “A knows that B knows that C knows that : : :” goes. Note that if one of the dragons missed your farewell announcement (which was “At least one the 100 dragons on this island has green eyes”), then they will all happily remain dragons throughout the ages. here I lost it. Does anybody has any ideas? They would be greatly appreciated.