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_3 -> u. p_3 <-> u. p -> q. ~p_3. p <-> t_3. q -> p.
p <-> q can be inferred via the biconditional introduction rule. q <-> p can be inferred via the biconditional introduction rule. p_3 -> u can be inferred via the biconditional elimination rule. p -> t_3 can be inferred via the biconditional elimination rule. u -> p_3 can be inferred via the biconditional elimination rule. t_3 -> p can be inferred via the biconditional elimination rule. ~u can be inferred via the biconditional elimination rule.