Consider the following premises. ~q_6. forall y_3: U_2(y_3) <-> U_1(y_3). U_1(a_12) <-> p_6. p_6 -> q_6. Can we infer U_2(a_12) from them? If possible, name the inference rules being used at each step.
 From forall y_3: U_2(y_3) <-> U_1(y_3) we can infer U_2(a_12) <-> U_1(a_12) via universal instantiation. From p_6 -> q_6, ~q_6 we can infer ~p_6 via modus tollens. From U_1(a_12) <-> p_6, ~p_6 we can infer ~U_1(a_12) via biconditional elimination. Finally, from U_2(a_12) <-> U_1(a_12), ~U_1(a_12) we can infer ~U_2(a_12) via biconditional elimination, which contradicts U_2(a_12). Therefore, the answer is no.