Consider the following premises. There is at least one z for which z is a taxi driver if and only if z will sleep. For all z, z will sleep or z will play squash. For all z, z is a taxi driver or z will not play squash. Can we infer the following from them? There is at least one z for which z is a taxi driver.
 From the fact that there is at least one z for which z is a taxi driver if and only if z will sleep we can infer that there is at least one z for which if z sleeps, then z is a taxi driver. From the fact that for all z, z is a taxi driver or z will not play squash we can infer that for all z, if z plays squash, then z is a taxi driver. Finally, from the fact that there is at least one z for which if z sleeps, then z is a taxi driver, that for all z, if z plays squash, then z is a taxi driver, and that for all z, z will sleep or z will play squash we can infer that there is at least one z for which z is a taxi driver. Therefore, the answer is yes.