static void web_contractRelation(Web web, S rel, S dest) {
  for (Pair<WebNode> p : web_relationsOfType(web, rel)) {
    new Matches m;
    if (startsWith(web_text(p.b), dest + " ", m)) {
      web_setRelationText(p, rel + " " + dest);
      web_setText(p.b, trim(m.get(0)));
    }
  }
}