Geb and Œdipus

It seems that in the Egyptian myth, Shu separates his married children Nut (Heaven) and Geb (Earth); in retaliation, Geb kills Shu (his father), marries Tefnut (his mother, since his wife Nut remains inaccessible to him), and usurps the throne. This is, of course, related to the myth of Kronos, but I suppose it's also the source of the Œdipus myth. The sphinx, then, is a reference to the source of the myth (Egypt) and its riddle is meant to say that the story is to be interpreted mythically rather than literally.