Consider the following premises. p_12 <-> r_3. ~p_12. p_8 <-> r_3. Can we infer p_8 from them? If possible, name the inference rules being used at each step.
 From p_12 <-> r_3, ~p_12 we can infer ~r_3 via biconditional elimination. Finally, from p_8 <-> r_3, ~r_3 we can infer ~p_8 via biconditional elimination, which contradicts p_8. Therefore, the answer is no.