static <A, B, C> LPair<C extends Collection<A>, B> pairsWhereLengthOfABiggerThan(Collection<Pair<C extends Collection<A>, B>> c, int n) {
  new LPair<C extends Collection<A>, B> l;
  for (Pair<C extends Collection<A>, B> p : unnull(c))
    if (p != null && l(p.a) > n)
      l.add(p);
  ret l;
}