Consider the following premises. If it is overcast, then Karen is a lawyer. Karen is not a lawyer. It is windy. If Karen were a lawyer, then it is overcast. Can we infer the following from them? If we can, name the inference rule being used: It is overcast.
 From the fact that if it is overcast, then Karen is a lawyer, and that if Karen were a lawyer, then it is overcast we can infer that it is overcast if and only if Karen is a lawyer via biconditional introduction. Finally, from the fact that it is overcast if and only if Karen is a lawyer, and that Karen is not a lawyer we can infer that it is not overcast via biconditional elimination, which contradicts that It is overcast. Therefore, the answer is no.