Consider the following premises. For all z, if z were an electrician, then z is making tea. For all z, z is not an electrician. There is at least one z for which z will make tea if and only if z is an electrician. Can we infer the following from them? If we can, name the inference rule being used: For all z, z will make tea.
 From the fact that there is at least one z for which z will make tea if and only if z is an electrician we can infer that there is at least one z for which if z makes tea, then z is an electrician via existential biconditional elimination. From the fact that for all z, if z were an electrician, then z is making tea, and that there is at least one z for which if z makes tea, then z is an electrician we can infer that there is at least one z for which z is an electrician if and only if z will make tea via existential biconditional introduction. Finally, from the fact that there is at least one z for which z is an electrician if and only if z will make tea, and that for all z, z is not an electrician we can infer that there is at least one z for which z will not make tea via existential biconditional elimination, which contradicts that For all z, z will make tea. Therefore, the answer is no.