The paradox is most interesting after only one day remains. On Friday, after Monday through Thursday have passed with no exam, the professor's declaration beco

The paradox is most interesting after only one day remains. On Friday, after Monday through Thursday have passed with no exam, the professor's declaration becomes "we will have an exam later today, but you will not know it until then." If the professor tells you this, do you know the exam will happen? If you can know it, then the professor was wrong (at least) about the second half of his prediction, which brings into question the first half.