anchor.diff:              |> DSet.mapReduce 
                   (fun (words,label) -> seq { for w in words -> w,label } )
                   (fun (word, labels) -> 
  -                    let histogram : int[] = Array.zeroCreate numLabels
  +                    let histogram : int[] = Array.zeroCreate numClasses
                       for l in labels do
                           histogram.[l] <- histogram.[l] + 1
                       word, histogram)
  
positive.code:         | _ -> 
              None
  
      let addWords (numLabels: int) (countsOrNull: Counts[]) (words: HashSet<string>, label: int) = 
          let counts = 
              if countsOrNull = null 
  
negative.code:         words |> Seq.iter (fun w -> counts.[label] |> add w 1)
          counts
  
      // Adds two intermediate dictionaries, at the final "reduce" step of the parallel fold.
      // Used only in the DSet version.        
      let addCounts (counts1: Counts[]) (counts2: Counts[]) =
          let ret = 
              Array.map2 (fun (lc1: Counts) (lc2: Counts) ->
  