What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? If Charles drives a car, then Sarah is writing a letter. Richard is not a server. If Sarah writes a letter, then Charles is driving a car. Charles is driving a car if and only if Richard is a server.
Charles is driving a car if and only if Sarah is writing a letter. Sarah is writing a letter if and only if Charles is driving a car. If Charles drives a car, then Richard is a server. If Richard were a server, then Charles is driving a car. Charles is not driving a car.