Consider the following premises. For all x_1, x_1 will not cook. There is at least one x_1 for which if x_1 drinks water, then x_1 is cooking. For all x_1, x_1 will drink water if and only if x_1 is a taxi driver. Can we infer the following from them? If we can, name the inference rule being used: For all x_1, x_1 is a taxi driver.
 From the fact that there is at least one x_1 for which if x_1 drinks water, then x_1 is cooking, and that for all x_1, x_1 will not cook we can infer that there is at least one x_1 for which x_1 will not drink water via existential modus tollens. Finally, from the fact that for all x_1, x_1 will drink water if and only if x_1 is a taxi driver, and that there is at least one x_1 for which x_1 will not drink water we can infer that there is at least one x_1 for which x_1 is not a taxi driver via existential biconditional elimination, which contradicts that For all x_1, x_1 is a taxi driver. Therefore, the answer is no.