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_13 <-> u_4. u_4 and q_5.
u_4 can be inferred via the simplification rule. q_5 can be inferred via the simplification rule. p_13 -> u_4 can be inferred via the biconditional elimination rule. u_4 -> p_13 can be inferred via the biconditional elimination rule.