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 x_4 for which x_4 will not listen to a song. For all x_4, x_4 will listen to a song if and only if x_4 is rich.
For all x_4, if x_4 listens to a song, then x_4 is rich can be inferred via the universal biconditional elimination rule. For all x_4, if x_4 were rich, then x_4 is listening to a song can be inferred via the universal biconditional elimination rule. There is at least one x_4 for which x_4 is not rich can be inferred via the existential biconditional elimination rule.