Consider the following premises. s <-> u. q_1 <-> s_3. w_2 or u. ~s_3. w_2 -> q_1. Can we infer ~s from them? If possible, name the inference rules being used at each step.
 From q_1 <-> s_3, ~s_3 we can infer ~q_1 via biconditional elimination. From w_2 -> q_1, ~q_1 we can infer ~w_2 via modus tollens. From w_2 or u, ~w_2 we can infer u via disjunctive syllogism. From s <-> u we can infer u -> s via biconditional elimination. Finally, from u -> s, u we can infer s via modus ponens, which contradicts ~s. Therefore, the answer is no.