What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: There is at least one z_2 for which if z_2 plays a game, then z_2 is a taxi driver. For all z_2, if z_2 plays a game, then z_2 is a taxi driver. For all z_2, if z_2 were a taxi driver, then z_2 is playing a game.
For all z_2, z_2 will play a game if and only if z_2 is a taxi driver can be inferred via the universal biconditional introduction rule. For all z_2, z_2 is a taxi driver if and only if z_2 will play a game can be inferred via the universal biconditional introduction rule. There is at least one z_2 for which z_2 will play a game if and only if z_2 is a taxi driver can be inferred via the existential biconditional introduction rule. There is at least one z_2 for which z_2 is a taxi driver if and only if z_2 will play a game can be inferred via the existential biconditional introduction rule.