Consider the following premises. Susan is not climbing a mountain. Susan is climbing a mountain if and only if Karen is poor. Richard is playing tennis if and only if Karen is poor. Richard is playing tennis. Can we infer the following from them? Linda is sad.
 From the fact that Susan is climbing a mountain if and only if Karen is poor, and that Susan is not climbing a mountain we can infer that Karen is not poor. From the fact that Richard is playing tennis if and only if Karen is poor, and that Karen is not poor we can infer that Richard is not playing tennis. From the fact that Richard is not playing tennis we can infer that Richard is not playing tennis or Linda is sad. Finally, from the fact that Richard is not playing tennis or Linda is sad, and that Richard is playing tennis we can infer that Linda is sad. Therefore, the answer is yes. Notice, however, that the premises were contradictory, so we can infer anything from them.