'Func<_ICursor__, _IResult<_ISplit<T>, _ICursorError<R>>>' does not contain a definition for 'DowncastClone' and no accessible extension method 'DowncastClone' accepting a first argument of type 'Func<_ICursor__, _IResult<_ISplit<T>, _ICursorError<R>>>' could be found (are you missing a using directive or an assembly reference?)