Consider the following premises. For all y_1, y_1 is a sailor if and only if y_1 is curious. For all y_1, y_1 is a writer or y_1 is not a sailor. For all y_1, if y_1 were a writer, then y_1 is curious. Can we infer the following from them? For all y_1, y_1 is a writer if and only if y_1 is a sailor.
 From the fact that for all y_1, y_1 is a writer or y_1 is not a sailor we can infer that for all y_1, if y_1 were a sailor, then y_1 is a writer. From the fact that for all y_1, y_1 is a sailor if and only if y_1 is curious we can infer that for all y_1, if y_1 were curious, then y_1 is a sailor. From the fact that for all y_1, if y_1 were a writer, then y_1 is curious, and that for all y_1, if y_1 were curious, then y_1 is a sailor we can infer that for all y_1, if y_1 were a writer, then y_1 is a sailor. Finally, from the fact that for all y_1, if y_1 were a writer, then y_1 is a sailor, and that for all y_1, if y_1 were a sailor, then y_1 is a writer we can infer that for all y_1, y_1 is a writer if and only if y_1 is a sailor. Therefore, the answer is yes.