Collections.reverse(l_subtrahendXs);
        Collections.reverse(l_subtrahendYs);
        l_polygonXs.addAll(l_subtrahendXs);
        l_polygonYs.addAll(l_subtrahendYs);

        // create an actual polygon
        b_positive = (l_subtrahendMaxY <= l_minuendMaxY) 
                && (l_subtrahendMinY <= l_minuendMinY);
        createPolygon(x_graphics, x_dataArea, x_plot, x_domainAxis, 
                x_rangeAxis, b_positive, l_polygonXs, l_polygonYs);