(define (empty? l)
  (= (length l) 0))
 
(define (tr mat)
  (define (prepare row)
    (if (empty? row) 
        (list)
        (cons (list)
              (prepare (cdr row)))))  
 
  (define (col-iter row tmat)
    (cond
      ((> (length row) 0)
       (cons (cons (car row)
                   (car tmat))
             (col-iter (cdr row)
                       (cdr tmat))))      
      (else null)))
 
  (define (row-iter mat tmat)
    (cond 
      ((> (length mat) 0) (row-iter (cdr mat)         
                                    (col-iter (car mat) 
                                              tmat)))       
      (else tmat)))
 
  (row-iter (reverse mat) 
            (prepare (car mat))))
 
(define (mul a b)
  (define (b-row-iter ra rtb)
    (if (empty? rtb)
        0
        (+ (* (car ra)
              (car rtb))
           (b-row-iter (cdr ra)
                       (cdr rtb)))))
 
  (define (col-iter ra tb)
    (if (empty? tb)
        null
        (cons (b-row-iter ra
                          (car tb))
              (col-iter ra
                        (cdr tb)))))
 
  (define (row-iter a tb)
    (if (empty? a) 
        (list)
        (cons (col-iter (car a)
                        tb)
              (row-iter (cdr a) 
                        tb))))
 
  (row-iter a 
            (tr b)))
 
(define a (list (list 1 2)
                (list 3 4)
                (list 5 6)
                (list 7 8)))
 
(define b (list (list 10 20 30)
                (list 40 50 60)))
(mul a b)