Consider the following premises. Richard is climbing a mountain if and only if Elisabeth is a janitor. If it is late, then Richard is climbing a mountain. It is not late. If Richard climbs a mountain, then Charles is a police officer. If Charles were a police officer, then it is late. Can we infer the following from them? If we can, name the inference rule being used: Elisabeth is not a janitor.
 From the fact that if Richard climbs a mountain, then Charles is a police officer, and that if Charles were a police officer, then it is late we can infer that if Richard climbs a mountain, then it is late via transitivity. From the fact that if it is late, then Richard is climbing a mountain, and that if Richard climbs a mountain, then it is late we can infer that it is late if and only if Richard is climbing a mountain via biconditional introduction. From the fact that it is late if and only if Richard is climbing a mountain, and that it is not late we can infer that Richard is not climbing a mountain via biconditional elimination. Finally, from the fact that Richard is climbing a mountain if and only if Elisabeth is a janitor, and that Richard is not climbing a mountain we can infer that Elisabeth is not a janitor via biconditional elimination. Therefore, the answer is yes.