anchor.diff:  
               //Make graph from vertix and edges lists
               let graph = new AdjacencyGraph<string, Edge<string>>();
  +            let clust_graph = new ClusteredAdjacencyGraph<string, Edge<string>>(graph);
  +            for vertex_cluster in gr.cluster_vertex do
  +               let cluster = clust_graph.AddCluster();
  +               for j in vertex_cluster do
  +                  cluster.AddVertex(j)|>ignore
               for i in gr.vertex do
                   graph.AddVertex(i)|>ignore
               for i in gr.edge do
  
positive.code:     let  mutable productions:Production list = []
      let  mutable starts = ""
      let mutable vertex:string list = []
      let mutable edge:(string*string*string) list = []    
      let mutable outPath = ""
  
  type FileDotEngine()  =
  
negative.code: 
      
              //Initialize Graphviz algorithm
              let graphViz = new GraphvizAlgorithm<string, Edge<string>>(clust_graph);
              let evHandler (evArgs:FormatVertexEventArgs<string>) =
                  evArgs.VertexFormatter.Comment <- evArgs.VertexFormatter.Label
              let evHandler2 (evArgs:FormatEdgeEventArgs<string,Edge<string>>) =
  