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: r -> q_11. q_11 or s_2. q_11 -> r. r or ~s_2.
s_2 -> r can be inferred via the rewriting rule. r <-> q_11 can be inferred via the biconditional introduction rule. q_11 <-> r can be inferred via the biconditional introduction rule.