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 takes a plane, then z is a scientist. For all z, z will take a plane if and only if z is a taxi driver. There is at least one z for which if z were a scientist, then z is a taxi driver.
There is at least one z for which if z takes a plane, then z is a taxi driver can be inferred via the existential transitivity rule. For all z, if z takes a plane, then z is a taxi driver can be inferred via the universal biconditional elimination rule. For all z, if z were a taxi driver, then z is taking a plane can be inferred via the universal biconditional elimination rule.