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: q <-> u. ~q. s_3 <-> t. ~t.
~q and ~t can be inferred via the conjunction rule. ~t and ~q can be inferred via the conjunction rule. q -> u can be inferred via the biconditional elimination rule. s_3 -> t can be inferred via the biconditional elimination rule. u -> q can be inferred via the biconditional elimination rule. t -> s_3 can be inferred via the biconditional elimination rule. ~u can be inferred via the biconditional elimination rule. ~s_3 can be inferred via the biconditional elimination rule.