Consider the following premises. u <-> w. r <-> t. r -> w. ~u. Can we infer ~t from them? If possible, name the inference rules being used at each step.
 From u <-> w, ~u we can infer ~w via biconditional elimination. From r -> w, ~w we can infer ~r via modus tollens. Finally, from r <-> t, ~r we can infer ~t via biconditional elimination. Therefore, the answer is yes.