static void web_moveRelations(WebNode src, WebNode dest) {
  if (src == dest) ret;
  Web web = src.web;
  assertSame(web, dest.web);
  
  for (Pair<WebNode> p : cloneList(web_relations(web))) {
    if (p.a == src && p.b != dest) {
      web.getRelation(dest, p.b).addLabels(web.getRelation(p).labels);
      web_deleteRelation(p.a, p.b);
    } else if (p.b == src && p.a != dest) {
      web.getRelation(p.a, dest).addLabels(web.getRelation(p).labels);
      web_deleteRelation(p.a, p.b);
    }
  }
}