[Y_Y]

What's so special about "literals"? They must be symbols in the sense that they can be evaluated. The fact that you've defined them so that they evaluate to something indistinguishable from the unevaluated form is neat, but it doesn't seem to me fundamental. We could have a lisp where you aren't allowed to evaluate a raw number, it would just be a little more awkward.

[lisper]

One could also have symbols that evaluate to themselves rather than some bound value. In fact, Common Lisp has exactly that: keywords.