Consider the following premises. Karen is curious if and only if Joseph is rich. Karen is not curious. If it is sunny, then Joseph is rich. Can we infer the following from them? If we can, name the inference rule being used: It is sunny.
 From the fact that Karen is curious if and only if Joseph is rich we can infer that if Joseph were rich, then Karen is curious via biconditional elimination. From the fact that if Joseph were rich, then Karen is curious, and that Karen is not curious we can infer that Joseph is not rich via modus tollens. Finally, from the fact that if it is sunny, then Joseph is rich, and that Joseph is not rich we can infer that it is not sunny via modus tollens, which contradicts that It is sunny. Therefore, the answer is no.