Deontic Logic

Abstract

An ancient paradox is about the famous Greek law teacher Protagoras and goes like this: Protagoras and Euathlus agree that the former is to instruct the latter in rhetoric and is to receive a certain fee which is to be paid if and only if Euathlus wins his first court-case (in some versions: as soon as he has won his first case). Well, Euathlus completed his course but did not take any law cases. Some time elapsed and Protagoras sued his student for the sum. The following arguments were presented to the judge in court.