Consider the following premises. For all z, if z were an artist, then z is making tea. If John makes tea, then John is an artist. For all z, if z makes tea, then z is an artist. Can we infer the following from them? If we can, name the inference rule being used: John is an artist if and only if John is making tea.
 From the fact that for all z, if z makes tea, then z is an artist, and that for all z, if z were an artist, then z is making tea we can infer that for all z, z will make tea if and only if z is an artist via universal biconditional introduction. From the fact that for all z, z will make tea if and only if z is an artist we can infer that John is making tea if and only if John is an artist via universal instantiation. From the fact that John is making tea if and only if John is an artist we can infer that if John were an artist, then John is making tea via biconditional elimination. Finally, from the fact that if John were an artist, then John is making tea, and that if John makes tea, then John is an artist we can infer that John is an artist if and only if John is making tea via biconditional introduction. Therefore, the answer is yes.