Consider the following premises. forall x_7: ~R_7(x_7). R_7(e) -> t. t -> R_7(e). Can we infer t from them? If possible, name the inference rules being used at each step.
 From forall x_7: ~R_7(x_7) we can infer ~R_7(e) via universal instantiation. From t -> R_7(e), R_7(e) -> t we can infer t <-> R_7(e) via biconditional introduction. Finally, from t <-> R_7(e), ~R_7(e) we can infer ~t via biconditional elimination, which contradicts t. Therefore, the answer is no.