Consider the following premises. There is at least one z for which z will play squash if and only if z will take a plane. For all z, z will take a plane and z is a writer. Can we infer the following from them? If we can, name the inference rule being used: For all z, z will not play squash.
 From the fact that for all z, z will take a plane and z is a writer we can infer that for all z, z will take a plane via universal simplification. From the fact that there is at least one z for which z will play squash if and only if z will take a plane we can infer that there is at least one z for which if z takes a plane, then z is playing squash via existential biconditional elimination. Finally, from the fact that there is at least one z for which if z takes a plane, then z is playing squash, and that for all z, z will take a plane we can infer that there is at least one z for which z will play squash via existential modus ponens, which contradicts that For all z, z will not play squash. Therefore, the answer is no.