Consider the following premises. p -> r_1. t or u_3. q -> p. u_3 -> q. t -> q. Can we infer r_1 from them? If possible, name the inference rules being used at each step.
 From t -> q, u_3 -> q, t or u_3 we can infer q via disjunction elimination. From q -> p, p -> r_1 we can infer q -> r_1 via transitivity. Finally, from q -> r_1, q we can infer r_1 via modus ponens. Therefore, the answer is yes.