anchor.diff:          let updateVertices() = 
               bStartVertex := !bEndVertex
               incr bEndVertex
  -
   
           let restoreContext() = 
               let oldType, oldTokens, oldWasElse = stack.Pop()
  
positive.code:                         if node.children.Length <= 1 then ""
                          else ",style=\"filled\",fillcolor=red"
                      out.WriteLine (sprintf "%d [label=\"%s\"%s]" !count label color)
                      interNodeToNumber.Add (node, !count)
                      !count, true
              
              let nodeNumber, isNew = getNodeNumber interNode
  
negative.code:             if data.Length > 1
              then 
                  let newData = mergeNodes data
                  vertexToInterNode.[vertex] <- [newData]
  
              //At this point length of vertexToInterNode.[vertex] always is equal to 1.
              let oldValue = vertexToInterNode.[vertex].Head
  