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_1. p_8 -> q_8. t_1 -> u_4. u_4 -> t_1. q_8 -> u_4.
~u_4 can be inferred via the modus tollens rule. p_8 -> u_4 can be inferred via the transitivity rule. q_8 -> t_1 can be inferred via the transitivity rule. t_1 <-> u_4 can be inferred via the biconditional introduction rule. u_4 <-> t_1 can be inferred via the biconditional introduction rule.