But circular != self-referential. Self-referential is a deeper property. If I have 2 mutually recursive functions, that's circular. For example, most parsers

But circular != self-referential. Self-referential is a deeper property. If I have 2 mutually recursive functions, that's circular. For example, most parsers have mutually recursive functions. There's nothing self-referential about them though. On the other hand, a C compiler written in C is self-referential. It confuses subject and object, which leads to some interesting paradoxes like the number for the "tab" character never appearing in the source code, as Ken Thompson points out. The Godel sentence is self-referential. It makes a claim about itself. The movie Synecdoche NY and some of Lewis Carroll's works (which figure heavily in GEB as I recall) are self-referential. The person writing the work appears in the work. Charlie Kaufman does this a lot -- the movie Adaption also has these properties. But I don't see that Bach's music is self-referential. The music doesn't write more music, or have any awareness of itself. Escher's two hands is self-referential, because it's confusing subject and object. But the staircases aren't self-referential.