Consider the following premises. Karen is not fast. For all z, if z were a politician, then z is fast. If Karen were fast, then Karen is a politician. Can we infer the following from them? If we can, name the inference rule being used: Karen is a politician.
 From the fact that for all z, if z were a politician, then z is fast we can infer that if Karen were a politician, then Karen is fast via universal instantiation. From the fact that if Karen were a politician, then Karen is fast, and that if Karen were fast, then Karen is a politician we can infer that Karen is a politician if and only if Karen is fast via biconditional introduction. Finally, from the fact that Karen is a politician if and only if Karen is fast, and that Karen is not fast we can infer that Karen is not a politician via biconditional elimination, which contradicts that Karen is a politician. Therefore, the answer is no.