Consider the following premises. For all x_9, x_9 is fast if and only if x_9 will drink water. For all x_9, if x_9 drinks water, then x_9 is a poet. There is at least one x_9 for which x_9 is not a poet. For all x_9, if x_9 were a poet, then x_9 is drinking water. Can we infer the following from them? If we can, name the inference rule being used: For all x_9, x_9 is fast.
 From the fact that for all x_9, if x_9 were a poet, then x_9 is drinking water, and that for all x_9, if x_9 drinks water, then x_9 is a poet we can infer that for all x_9, x_9 is a poet if and only if x_9 will drink water via universal biconditional introduction. From the fact that for all x_9, x_9 is a poet if and only if x_9 will drink water, and that there is at least one x_9 for which x_9 is not a poet we can infer that there is at least one x_9 for which x_9 will not drink water via existential biconditional elimination. Finally, from the fact that for all x_9, x_9 is fast if and only if x_9 will drink water, and that there is at least one x_9 for which x_9 will not drink water we can infer that there is at least one x_9 for which x_9 is not fast via existential biconditional elimination, which contradicts that For all x_9, x_9 is fast. Therefore, the answer is no.