(** * Addendum to the standard library of Coq *)
Require Export Omega.
Global Obligation Tactic := idtac.
Notation "[ x ; .. ; y ]" := (cons x .. (cons y nil) .. ).

Lemma cons_skipn :
forall A d i (l:list A),
i < length l ->
nth i l d :: skipn (S i) l = skipn i l.