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: There is at least one z for which z is not rich. For all z, if z takes a plane, then z is rich. For all z, if z were rich, then z is taking a plane.
There is at least one z for which z will not take a plane can be inferred via the existential modus tollens rule. For all z, z will take a plane if and only if z is rich can be inferred via the universal biconditional introduction rule. For all z, z is rich if and only if z will take a plane can be inferred via the universal biconditional introduction rule.