Consider the following premises. p_11 -> s. u or ~s_3. ~p_11. s -> p_11. s <-> u. Can we infer s_3 from them? If possible, name the inference rules being used at each step.
 From u or ~s_3 we can infer s_3 -> u via rewriting. From p_11 -> s, s -> p_11 we can infer p_11 <-> s via biconditional introduction. From p_11 <-> s, ~p_11 we can infer ~s via biconditional elimination. From s <-> u, ~s we can infer ~u via biconditional elimination. Finally, from s_3 -> u, ~u we can infer ~s_3 via modus tollens, which contradicts s_3. Therefore, the answer is no.