Consider the following premises. forall x_18: P_18(x_18). ~r. t -> r. Can we infer t from them? If possible, name the inference rules being used at each step.
 From forall x_18: P_18(x_18) we can infer P_18(a_18) via universal instantiation. Finally, from t -> r, ~r we can infer ~t via modus tollens, which contradicts t. Therefore, the answer is no.