Consider the following premises. q_16 -> w. r_4 -> q_16. q_16 -> r_4. w -> s. ~s. Can we infer r_4 from them?
 From r_4 -> q_16, q_16 -> r_4 we can infer r_4 <-> q_16. From w -> s, ~s we can infer ~w. From q_16 -> w, ~w we can infer ~q_16. From r_4 <-> q_16 we can infer r_4 -> q_16. Finally, from r_4 -> q_16, ~q_16 we can infer ~r_4, which contradicts r_4. Therefore, the answer is no.