Consider the following premises. For all y, if y sleeps, then y is sad. For all y, y is a taxi driver if and only if y is sad. For all y, if y were a taxi driver, then y is sleeping. Can we infer the following from them? For all y, if y were sad, then y is a taxi driver.
 From the fact that for all y, if y were a taxi driver, then y is sleeping, and that for all y, if y sleeps, then y is sad we can infer that for all y, if y were a taxi driver, then y is sad. Finally, from the fact that for all y, y is a taxi driver if and only if y is sad we can infer that for all y, if y were sad, then y is a taxi driver. Therefore, the answer is yes.