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