static void printTopTen(MultiSet ms) {
  printTopTen(ms, null);
}

// renderer = func(O) -> S
static void printTopTen(MultiSet ms, O renderer) {
  for (O o : ms.getTopTen())
    print(ms.get(o) + ": " + (renderer != null ? callF(renderer, o) : structureOrText(o)));
  print();
}