Consider the following premises. w_1 -> s_3. w or ~u. u or w_1. w -> r_6. r_6 -> s_3. Can we infer s_3 from them? If possible, name the inference rules being used at each step.
 From w or ~u we can infer u -> w via rewriting. From u -> w, w -> r_6 we can infer u -> r_6 via transitivity. From u -> r_6, r_6 -> s_3 we can infer u -> s_3 via transitivity. Finally, from u -> s_3, w_1 -> s_3, u or w_1 we can infer s_3 via disjunction elimination. Therefore, the answer is yes.