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