//protected Multimap<S2CellId, MarkedS2Point> _delegate() {
            //  return _delegate;
            //}

            /** Add a point to the index if it does not already exist. */

            public IEnumerator <System.Collections.Generic.KeyValuePair <S2CellId, MarkedS2Point> > GetEnumerator()
            {
                return(_delegate.GetEnumerator());
            }