Consider the following premises. For all y, y is an electrician. There is at least one y for which y is happy. For all y, y is happy if and only if y is a taxi driver. Can we infer the following from them? There is at least one y for which y is an electrician and y is a taxi driver.
 From the fact that for all y, y is happy if and only if y is a taxi driver we can infer that for all y, if y were happy, then y is a taxi driver. From the fact that for all y, if y were happy, then y is a taxi driver, and that there is at least one y for which y is happy we can infer that there is at least one y for which y is a taxi driver. Finally, from the fact that for all y, y is an electrician, and that there is at least one y for which y is a taxi driver we can infer that there is at least one y for which y is an electrician and y is a taxi driver. Therefore, the answer is yes.