def ns_key_at
import bend-collections@1.0.0.0/src/containers/balanced_search_tree.bend as BalancedSearchTreeimport Base
658def ns_key_at(~K: Data, s: NodeStore<K>, +i: Nat) -> NodeStore<K> & Maybe<&2, K>:
659 NS{limit, depth, cap, +used, tags, lefts, rights, parents, keys} = s
660 ns_key_ok(~K, limit, depth, cap, used, tags, lefts, rights, parents, keys, i, Nat.is_lt(i, used))