Consider the following premises. Sarah is an office clerk if and only if it is overcast. It is not overcast. If Sarah were an office clerk, then it is overcast. If Sarah were not an office clerk, then it is snowing. Can we infer the following from them? If we can, name the inference rule being used: It is not snowing.
 From the fact that Sarah is an office clerk if and only if it is overcast we can infer that if it is overcast, then Sarah is an office clerk via biconditional elimination. From the fact that if it is overcast, then Sarah is an office clerk, and that if Sarah were an office clerk, then it is overcast we can infer that it is overcast if and only if Sarah is an office clerk via biconditional introduction. From the fact that it is overcast if and only if Sarah is an office clerk, and that it is not overcast we can infer that Sarah is not an office clerk via biconditional elimination. Finally, from the fact that if Sarah were not an office clerk, then it is snowing, and that Sarah is not an office clerk we can infer that it is snowing via modus ponens, which contradicts that It is not snowing. Therefore, the answer is no.