def dotty (params = {})
      dotfile = "graph.dot"
      File.open(dotfile, "w") {|f|
        print_dotted_on(params, f)
      }
      system("dotty", dotfile)
    end
def dotty (params = {})
      dotfile = "graph.dot"
      File.open(dotfile, "w") {|f|
        print_dotted_on(params, f)
      }
      system("dotty", dotfile)
    end
Call dotty[http://www.graphviz.org] for the graph which is written to the
 file 'graph.dot' in the # current directory.