Consider the following premises. For all y, if y drinks water, then y is an astronaut. For all y, if y were an astronaut, then y is drinking water. For all y, if y drinks water, then y is an astronaut. Can we infer the following from them? If we can, name the inference rule being used: For all y, y will drink water if and only if y is an astronaut.
 From the fact that for all y, if y were an astronaut, then y is drinking water, and that for all y, if y drinks water, then y is an astronaut we can infer that for all y, y is an astronaut if and only if y will drink water via universal biconditional introduction. From the fact that for all y, y is an astronaut if and only if y will drink water we can infer that for all y, if y were an astronaut, then y is drinking water via universal biconditional elimination. Finally, from the fact that for all y, if y drinks water, then y is an astronaut, and that for all y, if y were an astronaut, then y is drinking water we can infer that for all y, y will drink water if and only if y is an astronaut via universal biconditional introduction. Therefore, the answer is yes.