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_6 <-> u_3. u_3 -> q_11. p_6 -> r_2. ~r_2. q_11 -> u_3.
~p_6 can be inferred via the modus tollens rule. u_3 <-> q_11 can be inferred via the biconditional introduction rule. q_11 <-> u_3 can be inferred via the biconditional introduction rule. p_6 -> u_3 can be inferred via the biconditional elimination rule. u_3 -> p_6 can be inferred via the biconditional elimination rule.