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);