Consider the following premises. w_1 -> p. q_6 -> s. t -> w_1. p -> q_6. Can we infer ~(t -> s) from them? If possible, name the inference rules being used at each step.
 From p -> q_6, q_6 -> s we can infer p -> s via transitivity. From t -> w_1, w_1 -> p we can infer t -> p via transitivity. Finally, from t -> p, p -> s we can infer t -> s via transitivity, which contradicts ~(t -> s). Therefore, the answer is no.