Consider the following premises. It is not cold. If Robert were a politician, then Susan is a janitor. Jessica is fast if and only if it is cold. If Susan were a janitor, then Robert is a politician. If Robert were a politician, then Jessica is fast. Can we infer the following from them? If we can, name the inference rule being used: Susan is a janitor.
 From the fact that Jessica is fast if and only if it is cold, and that it is not cold we can infer that Jessica is not fast via biconditional elimination. From the fact that if Robert were a politician, then Jessica is fast, and that Jessica is not fast we can infer that Robert is not a politician via modus tollens. From the fact that if Robert were a politician, then Susan is a janitor, and that if Susan were a janitor, then Robert is a politician we can infer that Robert is a politician if and only if Susan is a janitor via biconditional introduction. Finally, from the fact that Robert is a politician if and only if Susan is a janitor, and that Robert is not a politician we can infer that Susan is not a janitor via biconditional elimination, which contradicts that Susan is a janitor. Therefore, the answer is no.