static L<IfThen> nlLogic_safeLHSEvalsOnly_verbose(L<IfThen> rules) {
  new L<IfThen> l;
  for (IfThen r : unnull(rules))
    if (nlLogic_allLHSEvalsSafe(r))
      l.add(r);
    else
      print("Dropping eval-unsafe rule: " + r);
  ret l;
}