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

Lemma firstn_map_nth :
forall A d n m (l:list A),
m+n <= length l ->
firstn n (skipn m l) = map (fun i => nth i l d) (seq m n).