It means proto-Lisp. https://en.m.wiktionary.org/wiki/ur- https://en.m.wiktionary.org/wiki/ur- Now, to your original question. No idea which of the early Lisp

It means proto-Lisp. https://en.m.wiktionary.org/wiki/ur- https://en.m.wiktionary.org/wiki/ur- Now, to your original question. No idea which of the early Lisps qualify exactly as such, or until when.