Consider the following premises. There is at least one x_6 for which x_6 is a lawyer if and only if x_6 will take a plane. For all x_6, if x_6 takes a plane, then x_6 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_6 for which if x_6 were a lawyer, then x_6 is taking a plane.
We can infer this via the existential biconditional elimination rule. Therefore, the answer is yes.