Consider the following premises. There is at least one x_4 for which x_4 will read a book if and only if x_4 is a soldier. For all x_4, x_4 will read a book. Can we infer the following from them? There is at least one x_4 for which x_4 is a soldier.
 From the fact that there is at least one x_4 for which x_4 will read a book if and only if x_4 is a soldier we can infer that there is at least one x_4 for which if x_4 reads a book, then x_4 is a soldier. Finally, from the fact that there is at least one x_4 for which if x_4 reads a book, then x_4 is a soldier, and that for all x_4, x_4 will read a book we can infer that there is at least one x_4 for which x_4 is a soldier. Therefore, the answer is yes.