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, z is a janitor if and only if z will play squash. If Elisabeth were a janitor, then Linda is rich. Linda is not rich.
Elisabeth is not a janitor can be inferred via the modus tollens rule. For all z, if z were a janitor, then z is playing squash can be inferred via the universal biconditional elimination rule. For all z, if z plays squash, then z is a janitor can be inferred via the universal biconditional elimination rule.