What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Mary is a bartender if and only if William is an astronaut. If Barbara were a writer, then William is an astronaut. If Mary were a bartender, then Barbara is a writer.
If Mary were a bartender, then William is an astronaut. If Mary were a bartender, then William is an astronaut. If William were an astronaut, then Mary is a bartender.