Consider the following premises. s <-> r. ~s. r -> t. s or ~t. Can we infer t from them? If possible, name the inference rules being used at each step.
 From s <-> r we can infer s -> r via biconditional elimination. From s -> r, r -> t we can infer s -> t via transitivity. From s or ~t we can infer t -> s via rewriting. From t -> s, s -> t we can infer t <-> s via biconditional introduction. Finally, from t <-> s, ~s we can infer ~t via biconditional elimination, which contradicts t. Therefore, the answer is no.