What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: If Charles were a cashier, then Jennifer is playing tennis. For all x, if x were a cashier, then x is an artist. If Charles were an artist, then Charles is a cashier. Jennifer is not playing tennis.
Charles is not a cashier can be inferred via the modus tollens rule.