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: p_2 <-> s_4. s_4 or ~p_2.
p_2 -> s_4 can be inferred via the rewriting rule. p_2 -> s_4 can be inferred via the biconditional elimination rule. s_4 -> p_2 can be inferred via the biconditional elimination rule.