Don't you love generalizations like this?  Wouldn't you love to be able to conceive of all powers of perception?  Well, a little hubris can go a ways. . . .  One of the most provocative books of modern criticism begins "All literature tells one story... "  I like that generalization, too.  And it's useful enough to be true. That book is one of the sources for this treatment of Joyce's story.  The concept of levels has its sources, too.