Consider the following premises. p_6 or q_2. s_1 or ~q_2. s_1 or ~u_1. p_6 -> u_1. Can we infer ~s_1 from them?
 From s_1 or ~u_1 we can infer u_1 -> s_1. From p_6 -> u_1, u_1 -> s_1 we can infer p_6 -> s_1. From s_1 or ~q_2 we can infer q_2 -> s_1. Finally, from p_6 -> s_1, q_2 -> s_1, p_6 or q_2 we can infer s_1, which contradicts ~s_1. Therefore, the answer is no.