What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? If it is late, then Susan is a taxi driver. Elisabeth is a janitor if and only if Susan is a taxi driver. If Elisabeth were a janitor, then it is late.
If Elisabeth were a janitor, then Susan is a taxi driver. If Elisabeth were a janitor, then Susan is a taxi driver. If Susan were a taxi driver, then Elisabeth is a janitor.