static Web web_lower(Web web) {
  for (WebNode node : web.nodes) {
    web_lower_noindex(node);
  }
  web_reindex(web);
  web.labelsToUpper = false;
  ret web;
}

static void web_lower_noindex(WebNode node) {
  node.labels = map(f web_lower_x, node.labels);
}

static Lisp web_lower_x(Lisp l) {
  ret nempty(l.args) ? l : lisp(toLowerCase(l.head));
}