anchor.diff:  }
   
   /// Collects elements into a mutable result container.
  -type internal Collector<'T, 'R> = 
  +type ParCollector<'T, 'R> = 
       /// The number of concurrently executing tasks
       abstract DegreeOfParallelism : int 
       /// Gets an iterator over the elements.
  
positive.code:                     member self.SourceType = stream.SourceType
                      member self.PreserveOrdering = stream.PreserveOrdering
                      member self.Stream () = stream.Stream() 
                      member self.Apply<'S> (collector : Collector<'T, 'S>) =
                          let collector = 
                              { new Collector<'T, 'S> with
                                  member self.DegreeOfParallelism = degreeOfParallelism
                                  member self.Iterator() = collector.Iterator()
                                  member self.Result = collector.Result }
  
negative.code:                 member self.SourceType = stream.SourceType
                  member self.PreserveOrdering = true
                  member self.Stream () = stream.Stream() 
                  member self.Apply<'S> (collector : ParCollector<'T, 'S>) =
                      let collector = 
                          { new ParCollector<'T, 'S> with
                              member self.DegreeOfParallelism = collector.DegreeOfParallelism
                              member self.Iterator() = 
                                  collector.Iterator()
  