Consider the following premises. forall y: ~Q(y). Q(d) <-> t_2. u -> t_2. Can we infer u from them? If possible, name the inference rules being used at each step.
 From forall y: ~Q(y) we can infer ~Q(d) via universal instantiation. From Q(d) <-> t_2, ~Q(d) we can infer ~t_2 via biconditional elimination. Finally, from u -> t_2, ~t_2 we can infer ~u via modus tollens, which contradicts u. Therefore, the answer is no.