(define (znak? x)
  (member x '(+ - / *)))

(define (prioritet sym)
  (cond
    ((member sym '(< >)) 0)
    ((member sym '(+ -)) 1)
    ((member sym '(* /)) 2)))

(define (rpn lst)
  (define (checker list stack)
    (or
     (and (null? list) stack)
     (let ((x (car list)))
       (or
        (and (equal? x '<) (checker (cdr list) (cons x stack)))
        (and (znak? x) (if (and (not (null? stack)) (< (prioritet x) (prioritet (car stack))))
                           (cons (car stack) (checker list (cdr stack)))
                           (checker (cdr list) (cons x stack))))
        (and (equal? x '>)  (if (equal? (car stack) '< )
                                (checker (cdr list) (cdr stack))
                                (cons (car stack) (checker list (cdr stack)))))
        (cons x  (checker (cdr list) stack))))))
  (checker lst '()))