void CounterexampleAnalyzer::writeDotGraphToDisk(string filename, Visualizer& visualizer) {
  cout << "generating dot IO graph file for an abstract STG:"<<filename<<endl;
  string dotFile="digraph G {\n";
  dotFile+=visualizer.abstractTransitionGraphToDot();
  dotFile+="}\n";
  write_file(filename, dotFile);
}