While (+ 1 2) doesn't work in the basic system, it is possible to extend it entirely in Lisp so that it does work. You could use Church numerals to represent th

While (+ 1 2) doesn't work in the basic system, it is possible to extend it entirely in Lisp so that it does work. You could use Church numerals to represent the numbers, for example. I once did it by representing numbers as lists of hex digits because I was writing a 6809 assembler in Lisp and hex math made it convenient.