Consider the following premises. If Sarah were sad, then Charles is playing tennis. For all x_7, x_7 will play tennis if and only if x_7 will take a plane. Sarah is sad or Charles is taking a plane. Can we infer the following from them? Charles is not playing tennis.
 From the fact that for all x_7, x_7 will play tennis if and only if x_7 will take a plane we can infer that Charles is playing tennis if and only if Charles is taking a plane. From the fact that Charles is playing tennis if and only if Charles is taking a plane we can infer that if Charles takes a plane, then Charles is playing tennis. Finally, from the fact that if Sarah were sad, then Charles is playing tennis, that if Charles takes a plane, then Charles is playing tennis, and that Sarah is sad or Charles is taking a plane we can infer that Charles is playing tennis, which contradicts that Charles is not playing tennis. Therefore, the answer is no.