static void debugOn(String name) {
    try {
      Class c = getClass("main$" + name);
      if (c == null) c = getClass(name);
      Field field;
      while (true)
        try {
          field = c.getDeclaredField("debug");
          break;
        } catch  (NoSuchFieldException e) {
          c = c.getSuperclass();
        }
      field.setBoolean(null, true);
    } catch (Exception e) {
      e.printStackTrace();
      System.err.println("Cannot debug class " + name);
    }
  }