Consider the following premises. q_3 -> r_3. r_3 -> q_3. q_4 <-> q_3. Can we infer r_3 -> q_4 from them?
 From r_3 -> q_3, q_3 -> r_3 we can infer r_3 <-> q_3. From q_4 <-> q_3 we can infer q_3 -> q_4. From r_3 <-> q_3 we can infer r_3 -> q_3. Finally, from r_3 -> q_3, q_3 -> q_4 we can infer r_3 -> q_4. Therefore, the answer is yes.