Consider the following premises. For all y, y is not fast. Sarah is fast if and only if Patricia is a bartender. Can we infer the following from them? If we can, name the inference rule being used: Patricia is not a bartender.
 From the fact that for all y, y is not fast we can infer that Sarah is not fast via universal instantiation. Finally, from the fact that Sarah is fast if and only if Patricia is a bartender, and that Sarah is not fast we can infer that Patricia is not a bartender via biconditional elimination. Therefore, the answer is yes.