Consider the following premises. s_3 or q_2. s -> q_20. q_20 -> s. p -> ~q_20. q_2 -> s. s_3 -> q_20. Can we infer p from them? If possible, name the inference rules being used at each step.
 From s -> q_20, q_20 -> s we can infer s <-> q_20 via biconditional introduction. From s <-> q_20 we can infer s -> q_20 via biconditional elimination. From q_2 -> s, s -> q_20 we can infer q_2 -> q_20 via transitivity. From s_3 -> q_20, q_2 -> q_20, s_3 or q_2 we can infer q_20 via disjunction elimination. Finally, from p -> ~q_20, q_20 we can infer ~p via modus tollens, which contradicts p. Therefore, the answer is no.