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: For all y_4, if y_4 plays a game, then y_4 is playing tennis. For all y_4, y_4 will not play tennis. There is at least one y_4 for which if y_4 plays tennis, then y_4 is playing a game.
For all y_4, y_4 will not play a game can be inferred via the universal modus tollens rule. There is at least one y_4 for which y_4 will play tennis if and only if y_4 will play a game can be inferred via the existential biconditional introduction rule. There is at least one y_4 for which y_4 will play a game if and only if y_4 will play tennis can be inferred via the existential biconditional introduction rule.