Consider the following premises. u -> t_4. u_1 -> u. ~t or p. p -> u. t or u_1. Can we infer ~t_4 from them? If possible, name the inference rules being used at each step.
 From t or u_1, ~t or p we can infer u_1 or p via resolution. From u_1 -> u, p -> u, u_1 or p we can infer u via disjunction elimination. Finally, from u -> t_4, u we can infer t_4 via modus ponens, which contradicts ~t_4. Therefore, the answer is no.