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_1, if x_1 were a janitor, then x_1 is taking a plane. There is at least one x_1 for which if x_1 works, then x_1 is a janitor. For all x_1, x_1 will not take a plane.
For all x_1, x_1 is not a janitor can be inferred via the universal modus tollens rule. There is at least one x_1 for which if x_1 works, then x_1 is taking a plane can be inferred via the existential transitivity rule.