(* How to generate the multiple product for a constant *)
Fixpoint lgenk (n: nat) (k: K p) {struct n} : list (K p) :=
  match n  with
    O => nil
  | 1 => k :: nil
  | S n1 => k::lgenk n1 k
  end.

Lemma cbl_map_inv l v : cbl _ (map f l) v -> exists v1, cbl _ l v1 /\ v = f v1.