sclass AllOnAllWithUpdates<A, B> {
  new TreeMap<Long, A> aList;
  new TreeMap<Long, B> bList;
  LPair<LongRange> todo = new LinkedList;
  LPair<Long> todo2 = new LinkedList;

  synchronized void newA(A a) {
    aList.put(lastKeyOr0(aList)+1, a);
    addPair(todo, longRange_one(lastKey(aList)), longRange(0, lastKeyOr0(bList)+1));
  }
  
  synchronized void newB(B b) {
    bList.put(lastKeyOr0(bList)+1, b);
    addPair(todo, longRange(0, lastKeyOr0(aList)+1), longRange_one(lastKey(bList)));
  }
  
  synchronized void updateA(A a) {
    removeValue(aList, a);
    newA(a);
  }
  
  synchronized void updateB(B b) {
    removeValue(bList, b);
    newB(b);
  }
  
  synchronized Pair<A, B> next() {
    while licensed {
      while (empty(todo2)) {
        if (empty(todo)) null;
        Pair<LongRange> p = popFirst(todo);
        addAll(todo2, outerProduct_pairs(keys(subMap_longRange(aList, p.a)), keys(subMap_longRange(bList, p.b))));
      }
      Pair<Long> p = popFirst(todo2);
      A a = aList.get(p.a);
      B b = bList.get(p.b);
      if (a != null && b != null) ret pair(a, b);
    }
    null;
  }
}