anchor.diff:                      x.Enqueue o
   
                   contained.Remove e |> ignore
  -                current <- None
  +                current <- null
               
   
   
  
positive.code:                     | None -> ()
          )
  
      member x.CurrentAdapiveObject = current
          
  
      /// <summary>
  
negative.code:     // the contained set is useful for determinig if an element has
      // already been enqueued
      let contained = HashSet<IAdaptiveObject>()
      let mutable current : IAdaptiveObject = null
      let mutable currentLevel = 0
  
      let getAndClear (set : ICollection<'a>) =
  