Local Open Scope logic.
(*Require Import tweetnacl20140427.split_array_lemmas.*)

Lemma nth_force_lengthn':
forall (A : Type) (n i : nat) (xs : list A) (default d: A) (N: (n < length xs)%nat),
(0 <= i < n)%nat ->
@nth A i (@force_lengthn A n xs default) d = @nth A i xs d.