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: exists y_4: U(y_4) <-> S(y_4). forall y_4: U(y_4) <-> S(y_4).
forall y_4: U(y_4) -> S(y_4) can be inferred via the universal biconditional elimination rule. exists y_4: U(y_4) -> S(y_4) can be inferred via the existential biconditional elimination rule. forall y_4: S(y_4) -> U(y_4) can be inferred via the universal biconditional elimination rule. exists y_4: S(y_4) -> U(y_4) can be inferred via the existential biconditional elimination rule.