Consider the following premises. Elisabeth is reading a book if and only if Elisabeth is sad. Elisabeth is reading a book if and only if Richard is an office clerk. Elisabeth is sad or Richard is an office clerk. Can we infer the following from them? Elisabeth is not reading a book.
 From the fact that Elisabeth is reading a book if and only if Richard is an office clerk we can infer that if Richard were an office clerk, then Elisabeth is reading a book. From the fact that Elisabeth is reading a book if and only if Elisabeth is sad we can infer that if Elisabeth were sad, then Elisabeth is reading a book. Finally, from the fact that if Elisabeth were sad, then Elisabeth is reading a book, that if Richard were an office clerk, then Elisabeth is reading a book, and that Elisabeth is sad or Richard is an office clerk we can infer that Elisabeth is reading a book, which contradicts that Elisabeth is not reading a book. Therefore, the answer is no.