What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? If it snows, then Charles is a taxi driver. Charles is a taxi driver if and only if William is taking a plane. Mary is running if and only if it is snowing. William is taking a plane or Mary is running.
If Charles were a taxi driver, then William is taking a plane. If Mary goes running, then it is snowing. If William takes a plane, then Charles is a taxi driver. If it snows, then Mary is running.