Consider the following premises. John is not taking a plane. For all x_7, x_7 will take a plane if and only if x_7 is a writer. For all x_7, if x_7 takes a plane, then x_7 is a writer. Can we infer the following from them? John is not a writer.
 From the fact that for all x_7, x_7 will take a plane if and only if x_7 is a writer we can infer that for all x_7, if x_7 were a writer, then x_7 is taking a plane. From the fact that for all x_7, if x_7 takes a plane, then x_7 is a writer, and that for all x_7, if x_7 were a writer, then x_7 is taking a plane we can infer that for all x_7, x_7 will take a plane if and only if x_7 is a writer. From the fact that for all x_7, x_7 will take a plane if and only if x_7 is a writer we can infer that John is taking a plane if and only if John is a writer. Finally, from the fact that John is taking a plane if and only if John is a writer, and that John is not taking a plane we can infer that John is not a writer. Therefore, the answer is yes.