// find best threshold value to separate list1 (smaller values) from list2 (bigger values), minimizing false positives + false negatives
// returns (threshold, false positives, false negatives)
static T3<Double, Int, Int> findBestThreshold(Cl<Double> list1, Cl<Double> list2) {
  if (empty(list1) || empty(list2)) null;
  T3<Double, Int, Int> t = findThreshold_unmoved(list1, list2);
  LPair<Double, Bool> l = sortedByPairA(
    concatLists(toPairsA(list1, false), toPairsA(list2, true)));
  double threshold = t.a;
  int i = binarySearchResultToInsertionPoint(generalizedBinarySearch2(l, p -> cmp(p.a, threshold)));
  int falsePositives = t.b, falseNegatives = t.c;
  
  if (falsePositives > falseNegatives) {
    // TODO
  } else if (falseNegatives > falsePositives) {
    while (i+1 < l(l)) {
      Pair<Double, Bool> p = l2.get(i);
      threshold = avg(p.a, l2.get(i+1).a);
      if (p.a <= threshold) {
        if (p.b) --falsePositives; else --falseNegatives;
      }
    }
  }
  ret t3(threshold, falsePositives, falseNegatives);
}