/// <summary>
 /// Run FindAll on the wrapped collection with the indicated filter.
 /// The result will <b>not</b> be read-only.
 /// </summary>
 /// <param name="f"></param>
 /// <returns></returns>
 public IIndexedSorted <T> FindAll(Func <T, bool> f)
 {
     return(indexedsorted.FindAll(f));
 }