Fixpoint v2k (n : nat) : vect n -> kn n :=
match n return vect n -> kn n  with
| O => fun v : vect 0 => tt
| S n1  => fun v => let (v1,v2) := v in
('C[v1], v2k n1 v2)
end.

Lemma contra_const n lf M : hom n 1 M ->
#<lf, M># = [(lf [.] v2k n M)%Kn].