Consider the following premises. For all y, if y were a writer, then y is drinking water. For all y, if y drinks water, then y is a writer. There is at least one y for which y will not drink water. Can we infer the following from them? For all y, y is a writer.
 From the fact that for all y, if y drinks water, then y is a writer, and that for all y, if y were a writer, then y is drinking water we can infer that for all y, y will drink water if and only if y is a writer. Finally, from the fact that for all y, y will drink water if and only if y is a writer, and that there is at least one y for which y will not drink water we can infer that there is at least one y for which y is not a writer, which contradicts that For all y, y is a writer. Therefore, the answer is no.