Consider the following premises. For all y, y is an office clerk if and only if y will drink water. There is at least one y for which if y were an office clerk, then y is driving a car. For all y, if y drives a car, then y is drinking water. Can we infer the following from them? If we can, name the inference rule being used: There is at least one y for which y is an office clerk if and only if y will drink water.
 From the fact that there is at least one y for which if y were an office clerk, then y is driving a car, and that for all y, if y drives a car, then y is drinking water we can infer that there is at least one y for which if y were an office clerk, then y is drinking water via existential transitivity. From the fact that for all y, y is an office clerk if and only if y will drink water we can infer that for all y, if y drinks water, then y is an office clerk via universal biconditional elimination. Finally, from the fact that there is at least one y for which if y were an office clerk, then y is drinking water, and that for all y, if y drinks water, then y is an office clerk we can infer that there is at least one y for which y is an office clerk if and only if y will drink water via existential biconditional introduction. Therefore, the answer is yes.