Consider the following premises. s_4 <-> q. q -> t_2. r_4 -> s_4. ~t_2. Can we infer r_4 from them?
 From q -> t_2, ~t_2 we can infer ~q. From s_4 <-> q, ~q we can infer ~s_4. Finally, from r_4 -> s_4, ~s_4 we can infer ~r_4, which contradicts r_4. Therefore, the answer is no.