red black trees and other data structures

Hello,

I want to use one of Yap's data structures to store large amounts of data (such as frequency lists for strings).

I have two questions concerning this:

(1) How can I use red-black trees? The manual says a lot of things about them, e.g. that a new red-black tree can be created with rb_new(T), but it doesn't say which module to load.

I tried:

use_module(library(rb)).
use_module(library(redblack)).
use_module(library(redblacktrees)).

and many other names, but none of them worked.

(2) My main concern is memory efficency, i.e. the less memory a solution needs the better. Which data structure should I use?

Simon