(define (accumulate op initial sequence)
  (if (null? sequence)
      initial
      (op (car sequence)
          (accumulate op 
                      initial 
                      (cdr sequence)))))
(define (accumulate-n op init seqs)
  (if (null? (car seqs))
      '()
      (cons (accumulate op init (map car seqs))
            (accumulate-n op init (map cdr seqs)))))
(define (dot-product v w)
  (accumulate + 0 (map * v w)))
(define (matrix-*-vector m v)
  (map (lambda (w)
         (accumulate + 0 (accumulate-n * 1 (list v w)))) m))
(define (transpose mat)
  (accumulate-n cons '() mat))
(define (matrix-*-matrix m n)
  (let ((cols (transpose n)))
    (map (lambda (w)
         (matrix-*-vector cols w
          ))
         m)))
#| END |#