// 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> findThreshold_unmoved(Cl<Double> list1, Cl<Double> list2) {
  if (empty(list1) || empty(list2)) null;
  double threshold = avg(doubleMax(list1), doubleMin(list2));
  int falsePositives = countPred(list1, d -> d > threshold);
  int falseNegatives = countPred(list2, d -> d <= threshold);
  ret t3(threshold, falsePositives, falseNegatives);
}