Okay. Here is a riddle for you guys:
Three people have been captured by an executioner. He tells them that they will be put on one mask each, and that he has 2 red, and 2 blue masks. Then he says that if one of them can guess what color they have on their own mask, all three will go free. If one answers wrong, everybody gets killed.
- Person 1 gets a red mask. Person 2 and Person 3 sees this.
- Person 2 gets a blue mask. Person 3 sees this.
- Person 3 gets a red mask.
Now the question for you is: Who can with certainty know what color he has on his mask, and how?
Neither of the persons guess, and it is not the executioner