(* Get the constant part of a vector *)
Fixpoint const (n: nat): (vect n) -> K :=
match n return vect n -> K with
| O => fun a => a
| S n1 => fun l => let (l1,l2) := l in const n1 l2
end.
Notation "'C[ x ]" := (const _ x).

Lemma const_add n (x1 x2: vect n): 'C[x1 + x2] = ('C[x1] + 'C[x2])%f.
Fixpoint eq0 (n : nat) : vect n -> bool :=
match n return (vect n -> bool) with
| 0%nat => fun a => (a ?= 0)%f
| S n1 =>
fun l1 =>
let (l2, l3) := l1 in
if eq0 n1 l2 then eq0 n1 l3 else false
end.