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: forall x_6: P_6(x_6) <-> U_2(x_6). exists x_6: ~P_6(x_6). forall x_6: S(x_6) -> U_2(x_6).
forall x_6: P_6(x_6) -> U_2(x_6) can be inferred via the universal biconditional elimination rule. forall x_6: U_2(x_6) -> P_6(x_6) can be inferred via the universal biconditional elimination rule. exists x_6: ~U_2(x_6) can be inferred via the existential biconditional elimination rule.