Consider the following premises. For all x_6, if x_6 plays tennis, then x_6 is a politician. There is at least one x_6 for which if x_6 were a politician, then x_6 is playing tennis. For all x_6, if x_6 plays tennis, then x_6 is a politician. 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 x_6 is a politician if and only if x_6 will play tennis.
We can infer this via the existential biconditional introduction rule. Therefore, the answer is yes.