Consider the following premises. p_6 -> p. p_6. t -> r_1. p -> t. Can we infer r_1 from them?
 From p_6 -> p, p -> t we can infer p_6 -> t. From p_6 -> t, t -> r_1 we can infer p_6 -> r_1. Finally, from p_6 -> r_1, p_6 we can infer r_1. Therefore, the answer is yes.