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 working. For all x, x is not a janitor. For all x, if x works, then x is a janitor.
For all x, x will not work can be inferred via the universal modus tollens rule. For all x, x is a janitor if and only if x will work can be inferred via the universal biconditional introduction rule. For all x, x will work if and only if x is a janitor can be inferred via the universal biconditional introduction rule.