Consider the following premises. p <-> s. t_4 -> q. ~p. q -> s. s -> t_4. Can we infer q from them? If possible, name the inference rules being used at each step.
 From s -> t_4, t_4 -> q we can infer s -> q via transitivity. From p <-> s, ~p we can infer ~s via biconditional elimination. From s -> q, q -> s we can infer s <-> q via biconditional introduction. Finally, from s <-> q, ~s we can infer ~q via biconditional elimination, which contradicts q. Therefore, the answer is no.