Consider the following premises. John is a taxi driver if and only if it is raining. If it rains, then David is not a server. If Elisabeth climbs a mountain, then David is a server. Elisabeth is climbing a mountain. Can we infer the following from them? If we can, name the inference rule being used: John is not a taxi driver.
 From the fact that if Elisabeth climbs a mountain, then David is a server, and that Elisabeth is climbing a mountain we can infer that David is a server via modus ponens. From the fact that if it rains, then David is not a server, and that David is a server we can infer that it is not raining via modus tollens. Finally, from the fact that John is a taxi driver if and only if it is raining, and that it is not raining we can infer that John is not a taxi driver via biconditional elimination. Therefore, the answer is yes.