Fixpoint suml (l : list nat) : nat :=
  match l with
  | nil => 0
  | n :: l' => n + suml l'
  end.

Lemma Permutation_partition_list_nat b n l : (forall x, In x l -> b <= x < b + n) -> Permutation l (flat_map (fun n => filter (beq_nat n) l) (seq b n)).