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: For all x_10, if x_10 sleeps, then x_10 is a janitor. If John were a janitor, then Joseph is not playing a game. Joseph is playing a game.
John is not a janitor can be inferred via the modus tollens rule.