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_13: Q_13(x_13) -> S_1(x_13). forall x_13: S_1(x_13) -> Q_13(x_13). S_1(a_4) or ~u.
u -> S_1(a_4) can be inferred via the rewriting rule. forall x_13: Q_13(x_13) <-> S_1(x_13) can be inferred via the universal biconditional introduction rule. forall x_13: S_1(x_13) <-> Q_13(x_13) can be inferred via the universal biconditional introduction rule.