anchor.diff:    (- (window-current-linum window)
        (window-vtop-linum window)))
   
  -(defun window-cursor-y-if-wrapping (window)
  +(defun window-cursor-y (window)
     (+ (window-cursor-y-not-wrapping window)
        (window-wrapping-offset window)))
   
  
positive.code:   (if (minusp n)
        (scroll-down (- n))
        (dotimes (_ n t)
          (when (and (= (window-cursor-y-if-wrapping (current-window))
                        (- (window-height) 2))
                     (/= 1 (window-vtop-linum)))
            (unless (forward-line (- n))
  
negative.code:   (if (minusp n)
        (scroll-up (- n))
        (dotimes (_ n t)
          (when (= (window-cursor-y (current-window)) 0)
            (unless (forward-line n)
              (return nil)))
          (let ((prev-linum (window-vtop-linum))
  