How is catharsis used in Oedipus Rex?

An ancient Greek
audience, coming to the theater, would already be familiar with the fate of , the king doomed to
kill his father and marry and his mother.  Thus, the playwright's skill had less to do with
constructing unexpected plot twists or a surprising ending, for example, and more to do with
telling the story well.  One way to achieve this was through the use of dramatic: when the
audience knows...