Consider the following premises. For all y, if y reads a book, then y is a politician. For all y, if y were a politician, then y is a sailor. For all y, y will read a book if and only if y is a sailor. Can we infer the following from them? There is at least one y for which if is not true that y will read a book if and only if y is a sailor.
 From the fact that for all y, y will read a book if and only if y is a sailor we can infer that for all y, if y were a sailor, then y is reading a book. From the fact that for all y, if y reads a book, then y is a politician, and that for all y, if y were a politician, then y is a sailor we can infer that for all y, if y reads a book, then y is a sailor. Finally, from the fact that for all y, if y reads a book, then y is a sailor, and that for all y, if y were a sailor, then y is reading a book we can infer that for all y, y will read a book if and only if y is a sailor, which contradicts that There is at least one y for which if is not true that y will read a book if and only if y is a sailor. Therefore, the answer is no.