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 z_1, if z_1 listens to a song, then z_1 is working. For all z_1, z_1 will work if and only if z_1 will listen to a song. There is at least one z_1 for which z_1 will not listen to a song.
For all z_1, if z_1 works, then z_1 is listening to a song can be inferred via the universal biconditional elimination rule. For all z_1, if z_1 listens to a song, then z_1 is working can be inferred via the universal biconditional elimination rule. There is at least one z_1 for which z_1 will not work can be inferred via the existential biconditional elimination rule.