Consider the following premises. William is working if and only if Barbara is an office clerk. William is working if and only if Barbara is an office clerk. Can we infer the following from them? If we can, name the inference rule being used: If Barbara were an office clerk, then William is working.
 From the fact that William is working if and only if Barbara is an office clerk we can infer that if William works, then Barbara is an office clerk via biconditional elimination. Finally, from the fact that William is working if and only if Barbara is an office clerk we can infer that if Barbara were an office clerk, then William is working via biconditional elimination. Therefore, the answer is yes.