Hint Resolve f_pred_precise f_pred_positive.

Lemma Znth_join_hists : forall i lh (Hlen : Forall (fun h => Zlength h = size) lh),
Znth i (fold_right join_hists empty_hists lh) ([], []) =
(concat (map fst (map (fun h => Znth i h ([], [])) lh)),
concat (map snd (map (fun h => Znth i h ([], [])) lh))).