Consider the following premises. It is late. If Mary plays tennis, then it is late. If it is late, then Mary is playing tennis. Can we infer the following from them? Mary is playing tennis or Elisabeth is rich.
 From the fact that if Mary plays tennis, then it is late, and that if it is late, then Mary is playing tennis we can infer that Mary is playing tennis if and only if it is late. From the fact that Mary is playing tennis if and only if it is late we can infer that if it is late, then Mary is playing tennis. From the fact that if it is late, then Mary is playing tennis, and that it is late we can infer that Mary is playing tennis. Finally, from the fact that Mary is playing tennis we can infer that Mary is playing tennis or Elisabeth is rich. Therefore, the answer is yes.