SICP ex 2.51

(define (below painter1 painter2)
  (let ((split-point (make-vect 0.0 0.5)))
    (let ((paint-top
           (transform-painter painter1
                              split-point
                              (make-vect 1.0 0.5)
                              (make-vect 0.0 1.0)))
          (paint-bottom
           (transform-painter painter2
                              (make-vect 0.0 0.0)
                              (make-vect 1.0 0.0)
                              (make-vect 0.0 0.5))))
      (lambda (frame)
        (append (paint-top frame)
                (paint-bottom frame))))))

(define (below painter1 painter2)
  (rotate90 (beside (rotate270 painter1) (rotate270 painter2))))