(4vs-xor-lists x y) pairwise xors together the sexprs from two separate lists, forming a new sexpr list.
Function:
(defun 4vs-xor-lists (x y) (declare (xargs :guard (equal (len x) (len y)))) (if (atom x) nil (cons (4vs-xor (car x) (car y)) (4vs-xor-lists (cdr x) (cdr y)))))