Consider the following premises. If it is overcast, then Richard is a taxi driver. If it snows, then it is overcast. If Richard were a taxi driver, then it is overcast. Can we infer the following from them? If we can, name the inference rule being used: The fact that it snows does not imply that Richard is a taxi driver.
 From the fact that if Richard were a taxi driver, then it is overcast, and that if it is overcast, then Richard is a taxi driver we can infer that Richard is a taxi driver if and only if it is overcast via biconditional introduction. From the fact that Richard is a taxi driver if and only if it is overcast we can infer that if it is overcast, then Richard is a taxi driver via biconditional elimination. Finally, from the fact that if it snows, then it is overcast, and that if it is overcast, then Richard is a taxi driver we can infer that if it snows, then Richard is a taxi driver via transitivity, which contradicts that The fact that it snows does not imply that Richard is a taxi driver. Therefore, the answer is no.