Consider the following premises. t_3 <-> u. u <-> q_13. ~q_13. Can we infer t_3 from them? If possible, name the inference rules being used at each step.
 From u <-> q_13, ~q_13 we can infer ~u via biconditional elimination. Finally, from t_3 <-> u, ~u we can infer ~t_3 via biconditional elimination, which contradicts t_3. Therefore, the answer is no.