Consider the following premises. If Sarah sleeps, then John is working. It is raining if and only if it is snowing. Sarah is sleeping. If it rains, then John is not working. Can we infer the following from them? If we can, name the inference rule being used: It is snowing.
 From the fact that if Sarah sleeps, then John is working, and that Sarah is sleeping we can infer that John is working via modus ponens. From the fact that if it rains, then John is not working, and that John is working we can infer that it is not raining via modus tollens. Finally, from the fact that it is raining if and only if it is snowing, and that it is not raining we can infer that it is not snowing via biconditional elimination, which contradicts that It is snowing. Therefore, the answer is no.