!(set-env (letrec ((mapcar (lambda (f list)
                              (if (eq list nil)
                                  nil
                                  (cons (f (car list)) (mapcar f (cdr list))))))
                    (make-row (lambda (list)
                                (if (eq list nil)
                                    nil
                                    (let ((cdr (cdr list)))
                                      (cons (cons (car list) (car cdr))
                                            (make-row (cdr cdr)))))))
                    (make-tree-aux (lambda (list)
                                     (let ((row (make-row list)))
                                       (if (eq (cdr row) nil)
                                           row
                                           (make-tree-aux row)))))
                    (make-tree (lambda (list)
                                 (car (make-tree-aux list))))
                    (reverse-tree (lambda (tree)
                                    (if (atom tree)
                                        tree
                                        (cons (reverse-tree (cdr tree))
                                              (reverse-tree (car tree)))))))
             (current-env)))