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_2. u_2. q_15.
u_2 and q_15 can be inferred via the conjunction rule. q_15 and u_2 can be inferred via the conjunction rule. u_3 -> u_2 can be inferred via the biconditional elimination rule. u_2 -> u_3 can be inferred via the biconditional elimination rule.