Consider the following premises. ~q_26. ~t -> s_2. t <-> q_26. s_2 -> u. Can we infer u or s from them?
 From t <-> q_26, ~q_26 we can infer ~t. From ~t -> s_2, ~t we can infer s_2. From s_2 -> u, s_2 we can infer u. Finally, from u we can infer u or s. Therefore, the answer is yes.