Consider the following premises. For all z, z is not an electrician. Robert is an electrician if and only if William is a writer. For all x_25, x_25 will listen to a song and x_25 will play squash. Can we infer the following from them? If we can, name the inference rule being used: William is a writer.
 From the fact that for all x_25, x_25 will listen to a song and x_25 will play squash we can infer that Karen is listening to a song and Karen is playing squash via universal instantiation. From the fact that Karen is listening to a song and Karen is playing squash we can infer that Karen is listening to a song via simplification. From the fact that for all z, z is not an electrician we can infer that Robert is not an electrician via universal instantiation. Finally, from the fact that Robert is an electrician if and only if William is a writer, and that Robert is not an electrician we can infer that William is not a writer via biconditional elimination, which contradicts that William is a writer. Therefore, the answer is no.