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: ~t. u <-> r_3. t <-> u. q -> r_3. s.
~t and s can be inferred via the conjunction rule. s and ~t can be inferred via the conjunction rule. u -> r_3 can be inferred via the biconditional elimination rule. t -> u can be inferred via the biconditional elimination rule. r_3 -> u can be inferred via the biconditional elimination rule. u -> t can be inferred via the biconditional elimination rule. ~u can be inferred via the biconditional elimination rule.