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 for which z is a janitor if and only if z will play tennis. For all z, z will play tennis or z will not listen to a song.
For all z, if z listens to a song, then z is playing tennis can be inferred via the universal rewriting rule. There is at least one z for which if z were a janitor, then z is playing tennis can be inferred via the existential biconditional elimination rule. There is at least one z for which if z plays tennis, then z is a janitor can be inferred via the existential biconditional elimination rule.