sclass NLLogic_MultiThreadedEngine {

  bool unsafeEvals, showFailed;

  F0<NLLogicChecker_v2> makeLogicChecker;

  Pair<L<IfThen>, LS> rulesAndFacts;

  MultiMap<Int, ExecutedRule> executedRules = treeMultiMap();

  new MultiThreadStepper stepper;

  new LinkedHashSet<S> inputs;

  *(Pair<L<IfThen>, LS> *rulesAndFacts) {}

  void processInput(S input) {

    if (!inputs.add(input)) ret;

    temp tempSetTL(nlLogic_processInputOrFact_steppable_allowUnsafeEvals, unsafeEvals);

    stepper.add(nlLogic_processInputOrFact_steppable(makeLogicChecker(), input, false /*inputAsFact*/, 

      rulesAndFacts, new Collector<ExecutedRule>() {

        bool add(ExecutedRule r) {

          if (!showFailed && r.isFailed()) true;

          executedRules.put(ai_executedRuleScorer().get(r), r);

          for (S s : unnull(r.newInput))

            processInput(s);

          true;

        }

      }));

  };

  void seedInput(S input) { processInput(input); }

  void fullRun {

    stepAllWithStats_multiThreaded(stepper);

  }

  NLLogicChecker_v2 makeLogicChecker() {

    ret makeLogicChecker != null ? callF(makeLogicChecker) : new NLLogicChecker_v2;

  }

  L<ExecutedRule> executedRules() { ret executedRules.allValues(); }

}