Consider the following premises. If it snows, then it is windy. If Charles works, then it is snowing. It is snowing if and only if it is windy. If it is windy, then Charles is working. Can we infer the following from them? If is not true that it is snowing if and only if Charles is working.
 From the fact that it is snowing if and only if it is windy we can infer that if it is windy, then it is snowing. From the fact that if it snows, then it is windy, and that if it is windy, then it is snowing we can infer that it is snowing if and only if it is windy. From the fact that it is snowing if and only if it is windy we can infer that if it snows, then it is windy. From the fact that if it snows, then it is windy, and that if it is windy, then Charles is working we can infer that if it snows, then Charles is working. Finally, from the fact that if it snows, then Charles is working, and that if Charles works, then it is snowing we can infer that it is snowing if and only if Charles is working, which contradicts that If is not true that it is snowing if and only if Charles is working. Therefore, the answer is no.