Сформировать список из позиций элемента, заданного параметром X, в списке L

(DEFUN f()
    (princ "Vvedite parametr X: " )
    (setq x(read))
    (princ "Vvedite spisok L: " )
    (setq l(read))
    (POISK x l)
)
(DEFUN POISK (x l &optional (n 1))
    (COND
        ((EQUAL (CAR l) x) (LIST n))
        (t (POISK x (CDR l) (+ n 1)))
    )
)

(DEFUN POISK (x l &optional (n 1))
    (COND
        ((EQUAL (CAR l) x) (cons n (poisk x (cdr l) (+ n 1))))
        (t (POISK x (CDR l) (+ n 1)))))

(defun poisk (x w &optional (n 1))
  (cond ((null w) nil)
        ((equal (car w) x) (cons n (poisk x (cdr w) (+ n 1))))
        (t (poisk x (cdr w) (+ n 1)))))
 
> (poisk 4 '(8 3 4 6 4 1))
(3 5)

(defun poisk (x w &optional ac (n 1))
  (cond ((null w) (reverse ac))
        (t (poisk x
                  (cdr w)
                  (if (equal (car w) x) (cons n ac) ac)
                  (+ n 1)))))
 
> (poisk 4 '(8 3 4 6 4 1))
(3 5)

(defun poisk (x w &optional ac (n 1))
  (if w (poisk x
               (cdr w)
               (if (equal (car w) x) (cons n ac) ac)
               (+ n 1))
      (reverse ac)))
 
> (poisk 4 '(8 3 4 6 4 1))
(3 5)

(defun poisk (x w)
  (loop for a in w and b upfrom 1
        when (equal a x) collect b))
 
> (poisk 4 '(8 3 4 6 4 1))
(3 5)

(defun poisk (x w)
  (loop for a in w and b upfrom 1
        nconc (when (equal a x) `(,b))))
 
> (poisk 4 '(8 3 4 6 4 1))
(3 5)