static PTElement ai_parseBottomUpToTree(S input) {
  ret ai_parseBottomUpToTree(new AI_BottomUpParser1, input);
}

static PTElement ai_parseBottomUpToTree(AI_BottomUpParser1 parser, S input) {
  parser.parse(input);
  ret ai_parseBottomUpToTree(parser);
}

static PTElement ai_parseBottomUpToTree(AI_BottomUpParser1 parser) {
  AI_BottomUpParser1.Word w = parser.fullGroup();
  if (w == null) null;
  L<S> classes = withoutQuoted(w.classes);
  if (empty(classes)) null;
  ret ai_completeParseTree(parser, ChooseCategory(w, classes));
}