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_2 -> ~q_11. u_2 <-> r_2. p_11. p_11 -> q_11.
q_11 can be inferred via the modus ponens rule. u_2 -> r_2 can be inferred via the biconditional elimination rule. r_2 -> u_2 can be inferred via the biconditional elimination rule.