func (d *ltDom) findVertexByName(n vName) (*Root, Object) {
	if n == 0 {
		return nil, 0
	}
	if int(n) < len(d.p.rootIdx)+1 {
		return d.p.rootIdx[n-1], 0
	}
	return nil, d.objs[int(n)-len(d.p.rootIdx)-1]
}
func (d *ltDom) findVertexByName(n vName) (*Root, Object) {
	if n == 0 {
		return nil, 0
	}
	if int(n) < len(d.p.rootIdx)+1 {
		return d.p.rootIdx[n-1], 0
	}
	return nil, d.objs[int(n)-len(d.p.rootIdx)-1]
}
// findVertexByName returns the root/object named by n, or nil,0 for the pseudo-root.