Greater-than-or-equal test for characters
(char>= x y) is true if and only if the character code of
x is greater than or equal to that of y. See char-code.
The guard for char>= specifies that its arguments are characters.
Char>= is a Common Lisp function. See any Common Lisp documentation
for more information.
(defun char>= (x y)
(declare (xargs :guard (and (characterp x) (characterp y))))
(>= (char-code x) (char-code y)))