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 an electrician, then z is taking a plane. There is at least one z for which if z takes a plane, then z is an electrician. For all z, if z takes a plane, then z is an electrician.
For all z, z is an electrician if and only if z will take a plane can be inferred via the universal biconditional introduction rule. For all z, z will take a plane if and only if z is an electrician can be inferred via the universal biconditional introduction rule. There is at least one z for which z will take a plane if and only if z is an electrician can be inferred via the existential biconditional introduction rule. There is at least one z for which z is an electrician if and only if z will take a plane can be inferred via the existential biconditional introduction rule.