func (d *ltDom) link(v, w vName) {
	d.ancestor[w] = v
}
func (d *ltDom) link(v, w vName) {
	d.ancestor[w] = v
}
func ( d * ltDom ) link ( v , w vName ) { d . ancestor [ w ] = v }
// link is LINK from the papers.
link is LINK from the papers .