Consider the following premises. James is bored if and only if Elisabeth is a police officer. James is bored if and only if David is a bartender. David is not a bartender. Can we infer the following from them? If we can, name the inference rule being used: Elisabeth is a police officer.
 From the fact that James is bored if and only if David is a bartender, and that David is not a bartender we can infer that James is not bored via biconditional elimination. Finally, from the fact that James is bored if and only if Elisabeth is a police officer, and that James is not bored we can infer that Elisabeth is not a police officer via biconditional elimination, which contradicts that Elisabeth is a police officer. Therefore, the answer is no.