static <A> A lowestByField(Iterable<A> l, S field) {
  A lowest = null;
  O lowestValue = null;
  for (A a : unnull(l)) {
    O val = getOpt(a, field);
    if (lowest == null || cmp(val, lowestValue) < 0) {
      lowest = a;
      lowestValue = val;
    }
  }
  ret lowest;
}

static <A> A mapMethodLike lowestByField(S field, Iterable<A> l) {
  ret lowestByField(l, field);
}