Consider the following premises. Robert is a scientist if and only if it is overcast. Susan is not excited. Elisabeth is a cashier if and only if it is overcast. If Elisabeth were a cashier, then Susan is excited. Can we infer the following from them? If we can, name the inference rule being used: Robert is not a scientist.
 From the fact that if Elisabeth were a cashier, then Susan is excited, and that Susan is not excited we can infer that Elisabeth is not a cashier via modus tollens. From the fact that Elisabeth is a cashier if and only if it is overcast, and that Elisabeth is not a cashier we can infer that it is not overcast via biconditional elimination. Finally, from the fact that Robert is a scientist if and only if it is overcast, and that it is not overcast we can infer that Robert is not a scientist via biconditional elimination. Therefore, the answer is yes.