(* 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_scal n k lfs (x: vect n) : #<< lfs, k .* x >># = k .* #<< lfs , x >>#.