static void ai_buParser1_reconstructGrouping(AI_BottomUpParser1 parser, AI_BottomUpParser1.Word group, S category) {
  // a + b = c
  for (S a : keys(parser.groupingsByA))
    for (PairS bAndC : parser.groupingsByA.get(a)) {
      S b = bAndC.a, c = bAndC.b;
      if (contains(group.classes, c))
        print("Possible production: " + a + " + " + b + " = " + c);
    }
}