What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? If William writes a letter, then Patricia is playing squash. William is writing a letter if and only if Barbara is driving a car. If Patricia plays squash, then Barbara is driving a car.
If William writes a letter, then Barbara is driving a car. If William writes a letter, then Barbara is driving a car. If Barbara drives a car, then William is writing a letter.