the puzzle: "the puzzle is to find the flaw in the very compelling line of reasoning above." this includes determining exactly "why" and under "what conditions" that step is not correct, in order to be sure not to make this mistake in a more complicated situation where the misstep may not be so obvious. in short, the problem is to solve the paradox. thus, in particular, the puzzle is "not" solved by the very simple task of finding another way to calculate the probabilities that does not lead to a contradiction.