> The non-trivial part must be that at least one person knows more than they did before the statement.
I think that's what they meant by non-trivial. If the stranger tells them something they already know, that doesn't count.
You can assume that an individual person can count the blue dots they see, but they can't count their own dot. If they count 9 dots, then the true number must be either 9 or 10, so they already know the number can't be prime.
I think that's what they meant by non-trivial. If the stranger tells them something they already know, that doesn't count.
You can assume that an individual person can count the blue dots they see, but they can't count their own dot. If they count 9 dots, then the true number must be either 9 or 10, so they already know the number can't be prime.