Consider the following premises. q <-> u_2. u_1 <-> u_2. ~q. Can we infer ~u_1 from them? If possible, name the inference rules being used at each step.
 From q <-> u_2, ~q we can infer ~u_2 via biconditional elimination. Finally, from u_1 <-> u_2, ~u_2 we can infer ~u_1 via biconditional elimination. Therefore, the answer is yes.