Consider the following premises. If Richard were a soldier, then Charles is drinking water. If Thomas were poor, then Richard is a soldier. If Charles drinks water, then Thomas is poor. If Thomas were poor, then Charles is drinking water. Can we infer the following from them? Charles is drinking water if and only if Thomas is poor.
 From the fact that if Thomas were poor, then Richard is a soldier, and that if Richard were a soldier, then Charles is drinking water we can infer that if Thomas were poor, then Charles is drinking water. Finally, from the fact that if Charles drinks water, then Thomas is poor, and that if Thomas were poor, then Charles is drinking water we can infer that Charles is drinking water if and only if Thomas is poor. Therefore, the answer is yes.