anchor.diff:  open YC.FSA.FsaApproximation
   open YC.FSA.GraphBasedFsa
   
  -let lexerErrMsg = "Unexpected symbol: "
  -let parserErrMsg = "Syntax error. Unexpected token "
  -let undefinedVariableErrMsg = "undefined variable"
  +let lexerErrMsg = "Unexpected symbol:"
  +let parserErrMsg = "Syntax error. Unexpected token"
  +let undefinedVariableErrMsg = "Undefined variable"
   
   type DrawingGraph (vertices : IEnumerable<int>, edges : ResizeArray<TaggedEdge<int, string>>) =
       member this.Vertices = vertices
  
positive.code:                 |> Array.map 
                      (
                          function 
                              Smbl e -> (sprintf "%s%c" lexerErrMsg <| fst e), snd e |> getDocumentRange 
                              | e -> failwithf "Unexpected tokenization result: %A" e
                      )
                  |> Array.iter addLError 
  
negative.code:         , getDocumentRange: Position<'br> -> 'range
          , printAst: Tree<'TokenType> -> string -> unit
          , printOtherAst: OtherTree<'TokenType> -> string -> unit
          , semantic : _ option) = //as this =
  
      let lexingFinished = new Event<LexingFinishedArgs<'node>>()
      let parsingFinished = new Event<ParsingFinishedArgs>()
  