anchor.diff:      (cons (car list) (remove-nth (1- n) (cdr list)))))
   
   (defun insert-nth (n element list)
  +  "Insert element into list at nth place, increasing the length of the list.
  +
  +Example: (insert-nth 3 'x '(a b c d e)) => (A B C X D E)"
     (declare
       (type (integer 0) n)
       (type list list))
  -  "Insert element into list at nth place, increasing the length of the list.
  -
  -Example: (insert-nth 3 'x '(a b c d e)) => (A B C X D E)"
     (assert (>= n 0))
     (assert (>= (length list) n))
     (if (or (zerop n) (null list))
  
positive.code:       (cons (car list) (insert-nth (1- n) element (cdr list)))))
  
  (defun replace-nth (n element list)
    (declare
      (type (integer 0) n)
      (type list list))
    "Replaces element of list at nth place, not increasing the length of the list.
  
  Example: (replace-nth 3 'x '(a b c d e)) => (A B C X E)"
    (assert (>= n 0))
    (assert (>= (length list) n))
    (if (or (zerop n) (null list))
  
negative.code: ;; https://invisible-island.net/ncurses/man/form.3x.html
  
  (defun remove-nth (n list)
    "Remove element at nth place from the list, decreasing the length of the list.
  
  Example: (remove-nth 3 '(a b c d e)) => (A B C E)"
    (declare
      (type (integer 0) n)
      (type list list))
    (assert (>= n 0))
    (assert (> (length list) n))
    (if (or (zerop n) (null list))
  