Consider the following premises. R_19(a_19) <-> t. forall x_19: ~R_19(x_19). s_1 -> t. Can we infer ~s_1 or s from them? If possible, name the inference rules being used at each step.
 From forall x_19: ~R_19(x_19) we can infer ~R_19(a_19) via universal instantiation. From R_19(a_19) <-> t, ~R_19(a_19) we can infer ~t via biconditional elimination. From s_1 -> t, ~t we can infer ~s_1 via modus tollens. Finally, from ~s_1 we can infer ~s_1 or s via addition. Therefore, the answer is yes.