Consider the following premises. r_1 -> u. q_11 -> u. t or ~u. r_1 or q_11. Can we infer ~t from them? If possible, name the inference rules being used at each step.
 From r_1 -> u, q_11 -> u, r_1 or q_11 we can infer u via disjunction elimination. From t or ~u we can infer u -> t via rewriting. Finally, from u -> t, u we can infer t via modus ponens, which contradicts ~t. Therefore, the answer is no.