diff --git a/chapter2.lisp b/chapter2.lisp
index f39c12a..fa14ef6 100644
--- a/chapter2.lisp
+++ b/chapter2.lisp
@@ -129,3 +129,15 @@ and upper bound."
   (if (null l)
       ()
       (append (reverse-user (cdr l)) (list (car l)))))
+
+;; Exercise 2.21
+(defun square-list (items)
+  (if (null items)
+      nil
+      (cons (* (car items) (car items)) (square-list (cdr items)))))
+
+(defun square-list-map (items)
+  (map 'list #'(lambda (x) (* x x)) items))
+
+(defun square-list-mapcar (items)
+  (mapcar #'(lambda (x) (* x x)) items))