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: q_20 or ~s. ~q_20. t_2. s <-> q_20.
~s can be inferred via the disjunctive syllogism rule. ~q_20 and t_2 can be inferred via the conjunction rule. t_2 and ~q_20 can be inferred via the conjunction rule. s -> q_20 can be inferred via the rewriting rule. s -> q_20 can be inferred via the biconditional elimination rule. q_20 -> s can be inferred via the biconditional elimination rule. ~s can be inferred via the biconditional elimination rule.