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: u -> q_1. t_4 -> u. t_4 -> u. q_1 <-> t_4.
t_4 -> q_1 can be inferred via the transitivity rule. t_4 -> q_1 can be inferred via the transitivity rule. q_1 -> t_4 can be inferred via the biconditional elimination rule. t_4 -> q_1 can be inferred via the biconditional elimination rule.