Consider the following premises. It is not sunny. It is sunny if and only if Karen is fast. It is late if and only if Karen is fast. Can we infer the following from them? If we can, name the inference rule being used: It is late.
 From the fact that it is sunny if and only if Karen is fast, and that it is not sunny we can infer that Karen is not fast via biconditional elimination. Finally, from the fact that it is late if and only if Karen is fast, and that Karen is not fast we can infer that it is not late via biconditional elimination, which contradicts that It is late. Therefore, the answer is no.