Consider the following premises. r -> q_6. ~q_6. r <-> q_6. Can we infer ~r from them? If possible, name the inference rules being used at each step.
 From r <-> q_6 we can infer q_6 -> r via biconditional elimination. From q_6 -> r, r -> q_6 we can infer q_6 <-> r via biconditional introduction. Finally, from q_6 <-> r, ~q_6 we can infer ~r via biconditional elimination. Therefore, the answer is yes.