SICP Series-chapter 2.2.2

2.26

2.27

(defun deep-reverse(list)
    (cond ((null list) nil)
          ((not (listp list)) list)
          (t (append (deep-reverse (cdr list)) (list (deep-reverse (car list)))))))
2.28
(defun fringe(list)
    (cond ((null list) nil)
          ((not (consp list)) (list list))
          (t (append (fringe (car list))
                     (fringe (cdr list))))))

2.29

2.30
(defun square-tree(list)

  (cond ((null list) nil)
        ((not (listp list)) (list (* list list)))
        (append (square-tree (car list)) (square-tree (cdr list)))))
(defun square-treev2(list)
  (defun squarev2(x)
         (cond ((null x) nil)
               ((not (listp list)) (list (* list list)))
               (append (squarev2 (car list)) (squarev2 (cdr list)))))
  (mapcar #'squarev2 list))
2.32

(defun subsets (s)
  (if (null s)
    (list nil)
    (let ((rest (subsets (cdr s))))
      (append
        rest
        (mapcar (lambda (r)
                  (cons (car s) r))
                rest)))))