Consider the following premises. s -> q_11. q_11 -> s. p_6 -> p. ~p. q_11 <-> p_6. Can we infer s from them? If possible, name the inference rules being used at each step.
 From s -> q_11, q_11 -> s we can infer s <-> q_11 via biconditional introduction. From p_6 -> p, ~p we can infer ~p_6 via modus tollens. From q_11 <-> p_6, ~p_6 we can infer ~q_11 via biconditional elimination. Finally, from s <-> q_11, ~q_11 we can infer ~s via biconditional elimination, which contradicts s. Therefore, the answer is no.