Character equality without regard to case
For characters x and y, (char-equal x y) is true if and only if x and y are the same except perhaps for their case.
The guard on char-equal states that its arguments are both characters.
Char-equal is a Common Lisp function. See any Common Lisp documentation for more information.
Function: char-equal
(defun char-equal (x y) (declare (xargs :guard (and (characterp x) (characterp y)))) (eql (char-downcase x) (char-downcase y)))