sclass AIStrategy_Racer_RandomWithVary<A> extends AIStrategy<A> {
  // user must set
  F0<A> random;
  F1<A> vary;

  // user can set
  int discardEvery = 5000;
  
  // internal
  AIStrategy_RandomWithVariation<A> leader, overtaker;
  new Best<A> leadersBest;
  int roundsSinceChange;

  public bool step() { go(); false; }
  
  AIStrategy_RandomWithVariation newAI() {
    ret copyFields(this, new AIStrategy_RandomWithVariation, 'random, 'vary);
  }
  
  void go {
    if (tossACoin()) {
      if (leader == null) leader = newAI();
      A guess = leader.guess();
      if (guess == null) ret;
      double score = submit(guess);
      leader.updateBest(guess, score);
      leadersBest.put(guess, score);
    } else {
      if (overtaker == null) overtaker = newAI();
      A guess = overtaker.guess();
      if (guess == null) ret;
      double score = submit(guess);
      overtaker.updateBest(guess, score);
      if (score > leadersBest.score()) {
        // displace leader!
        if (verbose)
          print("Overtake at " + formatScore(overtaker.best.score()) + " vs " + formatScore(leadersBest.score()));
        leader = overtaker;
        overtaker = null;
        roundsSinceChange = 0;
      } else if (roundsSinceChange++ >= discardEvery) {
        // make new overtaker
        if (verbose)
          print("Discarding overtaker at " + formatScore(overtaker.best.score()) + " vs " + formatScore(leadersBest.score()));
        overtaker = null;
        roundsSinceChange = 0;
      }
    }
  }
}