What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Charles is fast. For all x, if x takes a plane, then x is a taxi driver. William is not a taxi driver. For all x, if x were a taxi driver, then x is taking a plane.
Charles is fast and William is not a taxi driver. William is not a taxi driver and Charles is fast. For all x, x will take a plane if and only if x is a taxi driver. For all x, x is a taxi driver if and only if x will take a plane.