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: u_3 -> u. u or ~q_2. u -> u_3.
q_2 -> u can be inferred via the rewriting rule. u_3 <-> u can be inferred via the biconditional introduction rule. u <-> u_3 can be inferred via the biconditional introduction rule.