Consider the following premises. For all x_4, x_4 will read a book if and only if x_4 will play squash. For all x_4, x_4 will play squash. Can we infer the following from them? Barbara is reading a book.
 From the fact that for all x_4, x_4 will read a book if and only if x_4 will play squash we can infer that for all x_4, if x_4 plays squash, then x_4 is reading a book. From the fact that for all x_4, if x_4 plays squash, then x_4 is reading a book, and that for all x_4, x_4 will play squash we can infer that for all x_4, x_4 will read a book. Finally, from the fact that for all x_4, x_4 will read a book we can infer that Barbara is reading a book. Therefore, the answer is yes.