anchor.diff:              member self.Apply<'S> (collector : Collector<'R, 'S>) =
                   let collector = 
                       { new Collector<'T, 'S> with
  +                        member self.DegreeOfParallelism = collector.DegreeOfParallelism
                           member self.Iterator() = 
                               let { Func = iter } as iterator = collector.Iterator()
                               {   Index = iterator.Index; 
  
positive.code:                 member self.Result = 
                      !resultRef }
  
          let stream = if stream.PreserveOrdering then stream.Stream() |> Stream.toSeq |> ofSeq |> withDegreeOfParallelism !stream.DegreeOfParallelism else stream
          stream.Apply collector
  
  
  
negative.code:         let results = new List<'State ref>()
          let collector = 
              { new Collector<'T, 'State> with
                  member self.DegreeOfParallelism = stream.DegreeOfParallelism
                  member self.Iterator() = 
                      let accRef = ref <| state ()
                      results.Add(accRef)
  