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 climbs a mountain, then y is a cashier. For all y, if y were a cashier, then y is climbing a mountain. There is at least one y for which if y were a mechanic, then y is a cashier. For all y, y will climb a mountain.
For all y, y is a cashier can be inferred via the universal modus ponens rule. There is at least one y for which if y were a mechanic, then y is climbing a mountain can be inferred via the existential transitivity rule. For all y, y will climb a mountain if and only if y is a cashier can be inferred via the universal biconditional introduction rule. For all y, y is a cashier if and only if y will climb a mountain can be inferred via the universal biconditional introduction rule.