anchor.diff:          this.AddEdge e |> ignore
   
   [<Struct>]
  -type GraphAction<'br when 'br:comparison> =
  +type GraphAction<'br(* when 'br:comparison*)> =
       val startAct: int
       val endActs: HashSet<int>
       val graph: GraphTokenValue<'br>
  
positive.code:     member this.EndPos = (snd t).end_offset
      member this.Label = fst t
  
  type GraphTokenValue<'br when 'br:comparison>() =
      inherit AdjacencyGraph<int,TokenEdge<'br>>()
  
      member this.AddEdgeForsed (e:TokenEdge<_>) =
  
negative.code: let printSmbString (x:char*Position<_>) = 
          (fst x).ToString() + "_br: " + (snd x).back_ref + "(" + (snd x).start_offset.ToString() + "," + (snd x).end_offset.ToString() + ")"
  
  type TokenEdge<'br(* when 'br:comparison*)>(s,e,t)=
      inherit TaggedEdge<int, char*Position<'br>>(s,e,t)
          
      member this.BackRef = (snd t).back_ref
  