Corollary index_of_rebase : forall m n k, 0 <= n <= Zlength m -> NoDup (map fst m) ->
  index_of (rebase m n) k = option_map (fun i => (i - n) mod Zlength m) (index_of m k).

Lemma sepcon_rebase : forall l m, 0 <= m <= Zlength l -> fold_right sepcon emp l = fold_right sepcon emp (rebase l m).