Consider the following premises. For all z, z will play a game if and only if z is a police officer. For all z, if z were a police officer, then z is playing a game. Can we infer the following from them? If we can, name the inference rule being used: For all z, z is a police officer if and only if z will play a game.
 From the fact that for all z, z will play a game if and only if z is a police officer we can infer that for all z, if z plays a game, then z is a police officer via universal biconditional elimination. Finally, from the fact that for all z, if z were a police officer, then z is playing a game, and that for all z, if z plays a game, then z is a police officer we can infer that for all z, z is a police officer if and only if z will play a game via universal biconditional introduction. Therefore, the answer is yes.