static void ai_buParser1_reconstructGrouping(AI_BottomUpParser1 parser, AI_BottomUpParser1.Word group, S category) {
  MultiMap<S> superClasses = reverseMultiMap(parser.subClasses);
  Set<S> classes = makeHull_optimized(superClasses, category);
  print("Starting class " + category + ", found classes: " + classes);
  
  // 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(classes, c))
        print("Possible production: " + a + " + " + b + " = " + c);
    }
}