static WebNode web_findForwardRelated(WebNode node, S relationLabel) {
  ret web_findForwardRelated(node, node.web.parseLabel(relationLabel));
}

static WebNode web_findForwardRelated(WebNode node, Lisp relationLabel) {
  ret web_findForwardRelated(node.web, node, relationLabel);
}

static WebNode web_findForwardRelated(Web web, WebNode node, Lisp relationLabel) {
  for (Pair<WebNode> p : keys(web.relations))
    if (p.a == node) {
      WebNode rel = web.relations.get(p);
      if (rel.hasLabel(relationLabel))
        ret p.b;
    }
  null;
}