(defun check (x &optional (l '(I V X L C D M)) (c 1))
    (cond ((null l) 0)
          ((eq x (car l)) c)
          (t (check x (cdr l) (+ c 1)))))

(defun f (L &optional (last 0)(c 0) (n nil) )
    (let ((ch (> (check (cadr L)) (check (car L))))
          (ch2 (= (check last) (check (cadr L)))))
     (cond ((null L) t )
         ;((null (cadr L)) T)
          ( (= (check (car L)) 0) nil )
          ( (>= c 3) nil )
          ( (and n (>= (check (cadr L)) (check (car L)))) nil)
          ( (and n ch2 ) nil)
          ( (and (> c 0) (not ch)) nil)
          ;( (and (> (check (cadr L) '(I X C M)) 0) ch2)  nil)
          ( (eq (car L) (cadr L)) (f (cdr L) (car L) (+ c 1) n) )
          ( t (f (cdr L) (car L) 0 ch)))))

(trace f)
;(trace check)

(print (f '( M C M X C I  )))