static SS zipTwoTokenizationsToCIMap_strict(LS l1, LS l2) {
  int n = l(l1);
  if (n != l(l2)) null;
  SS map = ciMap();
  for (int i = 1; i < n; i += 2)
    if (!strictPutIC(map, l1.get(i), l2.get(i)))
      null;
  ret map;
}