anchor.diff:      member this.EndPos = (snd t).end_offset
       member this.Label = fst t
   
  -type GraphTokenValue<'br when 'br:comparison>() =
  +type GraphTokenValue<'br(* when 'br:comparison*)>() =
       inherit AdjacencyGraph<int,TokenEdge<'br>>()
   
       member this.AddEdgeForsed (e:TokenEdge<_>) =
  
positive.code:         this.AddEdge e |> ignore
  
  [<Struct>]
  type GraphAction<'br when 'br:comparison> =
      val startAct: int
      val endActs: HashSet<int>
      val graph: GraphTokenValue<'br>
  
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
  