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 -> r. q_9 or t_1. q <-> q_9. r -> q.
t_1 -> q can be inferred via the transitivity rule. q -> q_9 can be inferred via the biconditional elimination rule. q_9 -> q can be inferred via the biconditional elimination rule.