Consider the following premises. Robert is an astronaut if and only if William is an electrician. For all x_7, x_7 is an astronaut if and only if x_7 is a politician. Robert is not a politician. Can we infer the following from them? If we can, name the inference rule being used: William is an electrician.
 From the fact that for all x_7, x_7 is an astronaut if and only if x_7 is a politician we can infer that Robert is an astronaut if and only if Robert is a politician via universal instantiation. From the fact that Robert is an astronaut if and only if Robert is a politician, and that Robert is not a politician we can infer that Robert is not an astronaut via biconditional elimination. Finally, from the fact that Robert is an astronaut if and only if William is an electrician, and that Robert is not an astronaut we can infer that William is not an electrician via biconditional elimination, which contradicts that William is an electrician. Therefore, the answer is no.