def points_from_y0x0y1x1(yxyx):
    """
    Construct a polygon representation from a rectangle described as a list [y0, x0, y1, x1]
    """
    y0 = yxyx[0]
    x0 = yxyx[1]
    y1 = yxyx[2]
    x1 = yxyx[3]
    return "%s,%s %s,%s %s,%s %s,%s" % (
        x0, y0,
        x1, y0,
        x1, y1,
        x0, y1
    )