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

Lemma nth_extensional {A}: forall l1 l2 (L:length l1 = length l2) (d:A)
(N: forall i, (0<=i<length l1)%nat -> nth i l1 d = nth i l2 d), l1=l2.