static L<GazelleTree> gazelle_getChildren(GazelleTree tree, O... _) {

  if (tree == null) null;

  if (tree.children != null) ret tree.children;

  tree.children = new L;

  double qualityCutOff = optPar qualityCutOff(_, -0.75);

  LS dialogHistory = cast optPar dialogHistory(_);

  bool debug = boolPar debug(_);

  // make rule engine etc.

  if (tree.ctx == null)

    tree.setContext(assertNotNull('evalContext, (GazelleEvalContext) callF(assertNotNull('makeEvalContext, (O) optPar makeEvalContext(_)))));

  GazelleEvalContext ctx = tree.ctx;

  RuleEngine2 engine = ctx.engine;

  SS inputMap = gazelle_inputMapFromLineAndHistory(tree.line, 

    concatLists(dialogHistory, tree.history()));

  if (boolPar respondingToHuman(_)) inputMap.put("_respondingToHuman" := "true");

  if (debug) print("inputMap=" + sfu(asTreeMap(inputMap)));

  // Splitters

  if (!boolPar skipSplitters(_)) for (RuleEngine2.SimplifyWithRule rule : engine.splitterRules()) pcall {

    Collection<S> out = gazelle_executeSplitterRule(engine, rule, tree.line);

    if (empty(out)) continue;

    GazelleTree child = new(joinWithVBar(out));

    child.ctx = ctx;

    child.isSplitNode = true;

    tree.add(child);

    for (S line : out)

      child.add(GazelleTree(line));

  }

  // Other rules

  bool firstConditionOnly = boolPar firstConditionOnly(_);

  O[] params = litobjectarray(debug := optPar debug(_), +tree);

  L<RuleEngine2_MatchedRule> l = sortByMethodDesc qualitySum(

    firstConditionOnly

      ? ai_ruleEngine2_rulesForInput_5(engine, inputMap, params)

      : ai_ruleEngine2_rulesForInput_5_allConditions(engine, inputMap, params));

  //print("Got rules: " + l(l));

  for (RuleEngine2_MatchedRule r : l) {

    double quality = r.relativeQuality();

    double cutOff = qualityCutOff;

    if (r.rule != null && r.rule.qualityCutOff != null) cutOff = r.rule.qualityCutOff;

    if (quality < cutOff && boolPar skipBad(_, true)) {

      if (debug) print("Match under quality (" + quality + "/" + qualityCutOff + "): " + r);

      continue;

    }

    S line = r.outText();

    GazelleTree child = new(line);

    child.ctx = ctx;

    child.mr = r;

    if (r.rule != null) child.lineType = r.rule.outType(); // TODO: there can be multiple out types

    gazelle_addPredictionToTreeNode(child);

    tree.add(child);

  }

  gazelle_sortChildren(tree);

  ret tree.children;

}