Consider the following premises. There is at least one y for which y is a poet if and only if y will take a plane. For all y, y will not take a plane. For all y, y is a sailor if and only if y is a poet. Can we infer the following from them? There is at least one y for which y is not a sailor.
 From the fact that there is at least one y for which y is a poet if and only if y will take a plane, and that for all y, y will not take a plane we can infer that there is at least one y for which y is not a poet. Finally, from the fact that for all y, y is a sailor if and only if y is a poet, and that there is at least one y for which y is not a poet we can infer that there is at least one y for which y is not a sailor. Therefore, the answer is yes.