static long longSum(Iterable<Long> l) {
  long sum = 0;
  for (Long i : unnull(l))
    if (i != null) sum += i;
  ret sum;
}

static <A> long lambdaMapLike longSum(IF1<A, Long> f, Iterable<A> l) {
  ret longSum(mapI(f, l));
}