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;

}