Section Test.
Variable (a b x y z : X).
(* The following goals should hold by computation *)
Goal fill [|Fin0; Fin1|] [|x;y;z|] [|a;b|] = [|a;b;z|].

Lemma fill_not_index I init V (i : Fin.t n) :
not_index I i ->
(fill I init V)[@i] = init[@i].