What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? John is playing tennis if and only if it is cloudy. If it rains, then it is cloudy. It is raining if and only if Barbara is writing a letter. John is not playing tennis.
If John plays tennis, then it is cloudy. If it rains, then Barbara is writing a letter. If it is cloudy, then John is playing tennis. If Barbara writes a letter, then it is raining. It is not cloudy.