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