static <A, B, C> L<A> lambdaMapLike pairsSortedByFunctionOnB(IF1<B, C> f, Iterable<Pair<A, B>> c) {
  LPair<A, B> l = cloneList(c);
  sort(l, (p1, p2) -> stdcompare(f.get(p1.b), f.get(p2.b)));
  ret l;
}