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 x_4, if x_4 listens to a song, then x_4 is working. For all x_4, if x_4 plays tennis, then x_4 is working. For all x_4, if x_4 works, then x_4 is playing tennis.
For all x_4, if x_4 listens to a song, then x_4 is playing tennis can be inferred via the universal transitivity rule. For all x_4, x_4 will play tennis if and only if x_4 will work can be inferred via the universal biconditional introduction rule. For all x_4, x_4 will work if and only if x_4 will play tennis can be inferred via the universal biconditional introduction rule.