Consider the following premises. forall x_8: R(x_8) or S_8(x_8). S_8(a) -> t. R(a) <-> t. Can we infer ~t from them? If possible, name the inference rules being used at each step.
 From forall x_8: R(x_8) or S_8(x_8) we can infer R(a) or S_8(a) via universal instantiation. From R(a) <-> t we can infer R(a) -> t via biconditional elimination. Finally, from R(a) -> t, S_8(a) -> t, R(a) or S_8(a) we can infer t via disjunction elimination, which contradicts ~t. Therefore, the answer is no.