(* Iterated contraction *)
Definition mcontra n (ll: list (kn n)) (x: vect n) :=
fold_left (fun x l => #<l,x>#) ll x.
Notation "#<< l , x >>#" := (mcontra _ l x).

Lemma mcontra_add n lfs (x y: vect n) :
#<< lfs, x + y >># = #<< lfs, x >># + #<< lfs,  y >>#.