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_2 or u. ~t_2. u -> q. q -> u.
u can be inferred via the disjunctive syllogism rule. u <-> q can be inferred via the biconditional introduction rule. q <-> u can be inferred via the biconditional introduction rule.