static Set<S> whatIs(S concept) {
  new HashSet<S> out;
  for (Lisp l : lispTruthByHead("fgvvrzypbkqomktd", "pggfeqzkqnezzfto"))
    if (eq(l.get(1), concept) && l.isLeaf(0))
      out.add(l.raw(0));
  ret out;
}