public Object clone() throws CloneNotSupportedException {
        SlidingGanttCategoryDataset clone
                = (SlidingGanttCategoryDataset) super.clone();
        if (this.underlying instanceof PublicCloneable) {
        	PublicCloneable pc = (PublicCloneable) this.underlying;
            clone.underlying = (GanttCategoryDataset) pc.clone();
        }
        return clone;