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 a bartender. For all x, x is not a lawyer. For all x, if x were a bartender, then x is a janitor. There is at least one x for which x is a janitor if and only if x is a lawyer.
For all x, x is a janitor if and only if x is a bartender can be inferred via the universal biconditional introduction rule. For all x, x is a bartender 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 a janitor, then x is a lawyer can be inferred via the existential biconditional elimination rule. There is at least one x for which if x were a lawyer, then x is a janitor can be inferred via the existential biconditional elimination rule. There is at least one x for which x is not a janitor can be inferred via the existential biconditional elimination rule.