Consider the following premises. It is windy if and only if it is snowing. If it is windy, then it is snowing. William is a janitor if and only if it is windy. Can we infer the following from them? If William were a janitor, then it is snowing.
 From the fact that it is windy if and only if it is snowing we can infer that if it snows, then it is windy. From the fact that William is a janitor if and only if it is windy we can infer that if William were a janitor, then it is windy. From the fact that if it is windy, then it is snowing, and that if it snows, then it is windy we can infer that it is windy if and only if it is snowing. From the fact that it is windy if and only if it is snowing we can infer that if it is windy, then it is snowing. Finally, from the fact that if William were a janitor, then it is windy, and that if it is windy, then it is snowing we can infer that if William were a janitor, then it is snowing. Therefore, the answer is yes.