Consider the following premises. For all y, y is a lawyer if and only if y is an office clerk. For all y, if y were an office clerk, then y is a lawyer. Can we infer the following from them? There is at least one y for which if is not true that y is an office clerk if and only if y is a lawyer.
 From the fact that for all y, y is a lawyer if and only if y is an office clerk we can infer that for all y, if y were a lawyer, then y is an office clerk. Finally, from the fact that for all y, if y were an office clerk, then y is a lawyer, and that for all y, if y were a lawyer, then y is an office clerk we can infer that for all y, y is an office clerk if and only if y is a lawyer, which contradicts that There is at least one y for which if is not true that y is an office clerk if and only if y is a lawyer. Therefore, the answer is no.