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_12: P_3(x_12) <-> S_12(x_12). S_12(a) <-> u. ~u.
S_12(a) -> u can be inferred via the biconditional elimination rule. u -> S_12(a) can be inferred via the biconditional elimination rule. ~S_12(a) can be inferred via the biconditional elimination rule. forall x_12: P_3(x_12) -> S_12(x_12) can be inferred via the universal biconditional elimination rule. forall x_12: S_12(x_12) -> P_3(x_12) can be inferred via the universal biconditional elimination rule.