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

Lemma skipn_hd : forall {A} n y (d:A),
n < length y ->
skipn n y = nth n y d :: skipn (S n) y.