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