if ((height != null) && (south != null)) height = Spring.sum(south, Spring.minus(y));
v = null; if ((height != null) && (south != null) && (y != null)) height = null;
    public void setY(Spring s)    {      y = s;      if ((height != null) && (south != null))        height = Spring.sum(south, Spring.minus(y));    }