} else if (NORTH.equals(constraint)) { container.remove(north);
} else if (NORTH.equals(constraint)) { if (viewport != component) { container.remove(north); }
    public void addSingletonComponent(SComponent component, Object constraint) {        if (VIEWPORT.equals(constraint)) {            container.remove(viewport);            viewport = component;        }        else if (NORTH.equals(constraint)) {            container.remove(north);            north = component;        }        else if (WEST.equals(constraint)) {            container.remove(west);            west = component;        }        else if (EAST.equals(constraint)) {            container.remove(east);            east = component;        }        else if (SOUTH.equals(constraint)) {            container.remove(south);            south = component;        }    }