static PTElement ai_parseBottomUpToTree(S input) {
  final new AI_BottomUpParser1 parser;
  parser.parse(s);
  AI_BottomUpParser1.Word w = parser.fullGroup();
  if (w == null) null;
  final L<WeightedProduction> productions = ai_buParser_parseWeightedProductions();
  ChooseCategory root = new(w, withoutQuoted(w.classes));
  ai_parseTree_makeWeights(parser, productions, root);
  ai_parseTree_makeTotalWeights(root, 1);
  ret root;
}