Tribune: ls
val ls : key -> int (* bits *) -> t -> key list
(* List up keys match with the given key prefix and the number of bits.
Suppose a Tribune tree [t] has bindings of keys K.
ls prefix bits t = { k_bits | k \in K, Segment.common_prefix prefix k = (prefix, Segment.empty, k_postfix), k_bits = sub k_postfix 0 bits }
*)
Edited by Jun Furuse