sclass AllOnAll<A, B> implements Producer<Pair<A, B>> {

  new L<A> aList;

  new L<B> bList;

  LPair<IntRange> todo = new LinkedList;

  LPair<A, B> todo2 = new LinkedList;

  void addA(A a) { newA(a); }

  void addAIfNotNull(A a) { if (a != null) newA(a); }

  synchronized void newA(A a) {

    add(aList, a);

    addPair(todo, intRange_last(aList), intRange(0, l(bList)));

  }

  synchronized void newAs(Iterable<A> l) {

    fOr (A a : l) newA(a);

  }

  void addB(B b) { newB(b); }

  void addBIfNotNull(B b) { if (b != null) newB(b); }

  synchronized void newB(B b) {

    add(bList, b);

    addPair(todo, intRange(0, l(aList)), intRange_last(bList));

  }

  synchronized void newBs(Iterable<B> l) {

    fOr (B b : l) newB(b);

  }

  public synchronized Pair<A, B> next() {

    while (empty(todo2)) {

      if (empty(todo)) null;

      Pair<IntRange> p = popFirst(todo);

      addAll(todo2, outerProduct_pairs(subList(aList, p.a), subList(bList, p.b)));

    }

    ret popFirst(todo2);

  }

  synchronized L cloneBList() {

    ret clonedList(bList);

  }

  L<A> getAs() { ret aList; }

  L<B> getBs() { ret bList; }

}