Consider the following premises. r -> t_2. u_1 or ~t_2. Can we infer r -> u_1 from them? If possible, name the inference rules being used at each step.
 From u_1 or ~t_2 we can infer t_2 -> u_1 via rewriting. Finally, from r -> t_2, t_2 -> u_1 we can infer r -> u_1 via transitivity. Therefore, the answer is yes.