Consider the following premises. For all x, if x were a mechanic, then x is a lawyer. There is at least one x for which x is a mechanic if and only if x is a lawyer. Can we infer the following from them? If we can, name the inference rule being used: There is at least one x for which x is a mechanic if and only if x is a lawyer.
That is one of the premises. Therefore, the answer is yes.