Consider the following premises. For all z, z will take a plane or z is not fast. There is at least one z for which z is not fast. For all z, z will take a plane if and only if z is fast. Can we infer the following from them? For all z, z will take a plane.
 From the fact that for all z, z will take a plane if and only if z is fast we can infer that for all z, if z takes a plane, then z is fast. From the fact that for all z, z will take a plane or z is not fast we can infer that for all z, if z were fast, then z is taking a plane. From the fact that for all z, if z were fast, then z is taking a plane, and that for all z, if z takes a plane, then z is fast we can infer that for all z, z is fast if and only if z will take a plane. Finally, from the fact that for all z, z is fast if and only if z will take a plane, and that there is at least one z for which z is not fast we can infer that there is at least one z for which z will not take a plane, which contradicts that For all z, z will take a plane. Therefore, the answer is no.