Consider the following premises. It is raining. It is raining if and only if Charles is climbing a mountain. Can we infer the following from them? Charles is climbing a mountain or it is overcast.
 From the fact that it is raining if and only if Charles is climbing a mountain we can infer that if it rains, then Charles is climbing a mountain. From the fact that if it rains, then Charles is climbing a mountain, and that it is raining we can infer that Charles is climbing a mountain. Finally, from the fact that Charles is climbing a mountain we can infer that Charles is climbing a mountain or it is overcast. Therefore, the answer is yes.