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, if x were a janitor, then x is rich. For all x, if x were rich, then x is a janitor. There is at least one x for which x is rich if and only if x is a janitor.
For all x, x is a janitor if and only if x is rich can be inferred via the universal biconditional introduction rule. For all x, x is rich if and only if x is a janitor can be inferred via the universal biconditional introduction rule. There is at least one x for which if x were rich, then x is a janitor can be inferred via the existential biconditional elimination rule. There is at least one x for which if x were a janitor, then x is rich can be inferred via the existential biconditional elimination rule.