However, we have no useful English operators to take the quoted words and change them into something else meaningfully. Though a non-English set can be argued to exist: http://creativeservices.iu.edu/resources/guide/marks.shtml If those were English themselves that would arguably complete the loop, but I would consider that stretching the point; these were explicitly invented to avoid the use of English and also translate to any other character-based language.
X-bar theory says that in all natural languages, Noun Phrases, Verb Phrases, and depending on who you read other types of phrases all have the same form; a single Head (which may be composite) and a Tail with zero or more elements. Never mind that they've just discovered S-expressions. The point is that in the natural language program:
multiply the radius squared and pi
But seriously, take a look at Quines and Hofstadter's Godel, Escher, Bach
(let ((let '`(let ((let ',let))
,let)))
`(let ((let ',let))
,let))