sclass HasKeyMap<A, B extends HasKey<A>> /*extends AbstractMap<A, B>*/ implements Iterable<B> {
  new Map<A, B> map;
  
  *() {}
  //*(Map<A, B> map) { putAll(this.map, map); }
  *(Iterable<B> l) { fOr (b : l) if (b != null) map.put(b.key(), b); }
  
  public Iterator<B> iterator() { ret valueIterator(map); }
  
  A firstKey() { ret main firstKey(map); }
}