code: def _find_furious_yaml(start, checked):
      
      directory = start
      while directory not in checked:
          checked.add(directory)
          for fs_yaml_name in FURIOUS_YAML_NAMES:
              yaml_path = os.path.join(directory, fs_yaml_name)
              if os.path.exists(yaml_path):
                  return yaml_path
          directory = os.path.dirname(directory)
      return None
docs: Traverse the directory tree identified by start
      until a directory already in checked is encountered or the path
      of furious.yaml is found.
  
      Checked is present both to make the loop termination easy
      to reason about and so the same directories do not get
      rechecked
  
      Args:
          start: the path to start looking in and work upward from
          checked: the set of already checked directories
  
      Returns:
          the path of the furious.yaml file or None if it is not found