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 y, if y were a writer, then y is taking a plane. For all y, y is not a police officer. There is at least one y for which if y takes a plane, then y is a cashier. For all y, if y were a cashier, then y is a police officer.
For all y, y is not a cashier can be inferred via the universal modus tollens rule. There is at least one y for which if y takes a plane, then y is a police officer can be inferred via the existential transitivity rule. There is at least one y for which if y were a writer, then y is a cashier can be inferred via the existential transitivity rule.