code: public static <T> void write(final String fileName, final Graph<T> graph) throws IOException {
      write(new File(fileName.endsWith(".dot") ? fileName : fileName + ".dot"), graph);
    }
docs: Writes a given formula's internal data structure as a dimacs file.
  @param fileName the file name of the dimacs file to write
  @param graph    the graph
  @param <T>      the type of the graph content
  @throws IOException if there was a problem writing the file