* composites the key sets from all of the composited maps.
*
* @return a set view of the keys contained in this map.
*/
public Set keySet() {
CompositeSet keys = new CompositeSet();
for (int i = this.composite.length - 1; i >= 0; --i) {
keys.addComposited(this.composite[i].keySet());
}
return keys;
}