// extensive version (better results) with full search
    
static class LCombineTwoFunctions2 extends LearnerImpl {
  static boolean debug;
  static long instances;
  Stepper stepper;
  new List<O[]> examples;
  
  *() {
    ++instances; 
    if (debug)
      debug("Instances: " + instances);
  }
  public void finalize() {--instances; }
  
  public void processInOut(O in, O out) {
    examples.add(new O[] {in, out});
    
    if (stepper == null)
      stepper = new Stepper(allFunctions());

    while (!stepper.ended()) {
      long time = System.currentTimeMillis();
      boolean b = check(stepper.current());
      time = System.currentTimeMillis()-time;
      if (debug) debug("check time: " + time);
      if (b)
        ret; // ok, keep
      else
        stepper.step();
    }
    
    fail();
  }
  
  boolean check(Function[] fg) {
    if (debug) {
      debug("Examples: " + examples.size() + ", stepper size: " + stepper.functions.size());
      debug("Checking " + structure(fg));
    }
    for (O[] e : examples) {
      O o = tryProcess(fg[0], e[0]);
      if (o != null) {
        O x = tryProcess(fg[1], o);
        if (e[1].equals(x))
          continue; // example ok
      }
      ret false;
    }
    ret true; // all examples ok
  }
  
  public O processIn(O in) {
    Function[] fg = stepper.current();
    ret fg[1].process(fg[0].process(in));
  }
  
  static O tryProcess(Function f, O in) null on exception {
    ret f.process(in);
  }
  
  static class Stepper {
    List<Function> functions;
    int i1, i2;
    
    *(List<Function> *functions) {}
    
    boolean ended() {
      ret i1 >= functions.size();
    }
    
    Function[] current() {
      ret new Function[] {functions.get(i1), functions.get(i2)};
    }
    
    void step() {
      if (i2 < functions.size()-1) ++i2;
      else { ++i1; i2 = 0; }
    }
  }
}

Began life as a copy of #1000500