static L<Pair<AI_BottomUpParser1.Word>> ai_buParser1_reconstructedGroupings(AI_BottomUpParser1 parser, AI_BottomUpParser1.Word group, S category) {
  L<Pair<AI_BottomUpParser1.Word>> l = new L;
  if (group == null || !group.isGroup()) ret l;
  
  // add subclasses of outer category
  MultiMap<S> finerClasses = reverseMultiMap(parser.subClasses);
  Set<S> classes = makeHull_optimized(finerClasses, 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(classes, c)) {
        //print("Possible production: " + a + " + " + b + " = " + c);
        for (L<AI_BottomUpParser1.Word> parts : group.constituents) {
          if (l(parts) != 2) continue; // shouldn't happen
          AI_BottomUpParser1.Word partA = first(parts), partB = second(parts);
          if (!contains(partA.classes, a)) continue;
          if (!contains(partB.classes, b)) continue;
          l.add(pair(partA, partB));
          //print("  Found grouping: " + partA.text + " + " + partB.text);
        }
      }
    }
  
  ret l;
}