static void web_mergeNodesByFirstLabel(Web web) {
  new HashMap<Lisp, WebNode> index;
  for (WebNode node : web.nodes)
    if (nempty(node.labels)) index.put(first(node.labels), node);
  
  for (WebNode node : cloneList(web.nodes)) if (nempty(node.labels)) {
    WebNode n = index.get(first(node.labels));
    if (n == node) continue;
    web_copyRelations(node, n);
    web.removeNode(node);
  }
}