Consider the following premises. s_1 -> q. q -> u. u -> p_4. w -> r_11. p_4 -> w. Can we infer s_1 -> r_11 from them?
 From p_4 -> w, w -> r_11 we can infer p_4 -> r_11. From s_1 -> q, q -> u we can infer s_1 -> u. From s_1 -> u, u -> p_4 we can infer s_1 -> p_4. Finally, from s_1 -> p_4, p_4 -> r_11 we can infer s_1 -> r_11. Therefore, the answer is yes.