From Undecidability.L Require Import LTactics.
Fixpoint many_lam k s := match k with 0 => s | S k => lam (many_lam k s) end.
Fixpoint many_app k s (v : Vector.t term k) :=
match v with
| Vector.nil => s
| Vector.cons x _ v => many_app (L.app s x) v
end.
Definition many_vars k := (tabulate (n := k) (fun i => k - S (proj1_sig (Fin.to_nat i)))).

Lemma many_vars_S n :
many_vars (S n) = n :: many_vars n.