It's the pervasive theme in the book, but never really given a conceptual grounding further than "this sort of looks like recursion or can be modelled circularly so it's a strange loop". The vagueness of it reveals itself as being "more intuitive", because a vaguer pattern will have more matches. I don't remember Hofstadter digressing on whether these loops work "in reverse" either, which is sort of what the author here is denying. Basically positing that f doesn't have a well-defined inverse.