def drawDoubleArrow(draw, xy, span):
    """
    Draws a double arrow between two points.
    """
    arrow_size = min(40, span)
    draw.line((xy[0], xy[1], xy[0], xy[1] + arrow_size), fill='white', width=3)
    draw.line((xy[0], xy[1] + arrow_size / 2, xy[0] + arrow_size / 2, xy[1]
        ), fill='white', width=3)
    draw.line((xy[0], xy[1] + arrow_size / 2, xy[0] + arrow_size / 2, xy[1] +
        arrow_size), fill='white', width=3)
    draw.line((xy[0] + span, xy[1] + arrow_size / 2, xy[0] + span - 
        arrow_size / 2, xy[1]), fill='white', width=3)
    draw.line((xy[0] + span, xy[1] + arrow_size / 2, xy[0] + span - 
        arrow_size / 2, xy[1] + arrow_size), fill='white', width=3)
    draw.line((xy[0], xy[1] + arrow_size / 2, xy[0] + span, xy[1] + 
        arrow_size / 2), fill='white', width=3)
    draw.line((xy[0] + span, xy[1], xy[0] + span, xy[1] + arrow_size), fill
        ='white', width=3)
