Sometimes known as Forrester’s paradox. It proves that if you murder someone, then you only did what you ought to do. For if you murder someone, then you ought to murder them gently. If you ought to murder them gently, then you ought to murder them. So, if you murder someone, then you ought to murder them. This is one of a number of such paradoxes. One version is that if someone does something, such as committing a crime, then there is an obligation on someone else, such as the police, to know about it, and deduces from that obligation that the original action was itself obligatory.