Consider the following premises. s_1 -> q_21. s or s_1. forall x: W_4(x). s <-> q_21. Can we infer ~q_21 from them? If possible, name the inference rules being used at each step.
 From s <-> q_21 we can infer s -> q_21 via biconditional elimination. From forall x: W_4(x) we can infer W_4(h) via universal instantiation. Finally, from s -> q_21, s_1 -> q_21, s or s_1 we can infer q_21 via disjunction elimination, which contradicts ~q_21. Therefore, the answer is no.