What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? David is working or it is raining. If it is late, then it is raining. If David works, then it is late. If it rains, then it is late.
If David works, then it is raining. It is late. It is late if and only if it is raining. It is raining if and only if it is late.