What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all z, z is a carpenter if and only if z is a taxi driver. There is at least one z for which z is a carpenter if and only if z is a janitor.
For all z, if z were a carpenter, then z is a taxi driver. There is at least one z for which if z were a carpenter, then z is a janitor. For all z, if z were a taxi driver, then z is a carpenter. There is at least one z for which if z were a janitor, then z is a carpenter.