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