static void ai_spec_searchForAnswer(S s) {
  L<S> cluster = ll(s);
  cluster = ai_cluster_forward(cluster, "parses to triple");
  if (empty(cluster)) ret;
  ai_expandCluster(cluster);
  cluster = ai_cluster_backward(cluster, "answers");
  if (empty(cluster)) ret;
  for (S a : cluster)
    ai_postTriple(a, "answers", s);
}