code: def notebooks_in_git_index(fmt):
      
      git_status = system('git', 'status', '--porcelain')
      re_modified = re.compile(r'^[AM]+\s+(?P<name>.*)', re.MULTILINE)
      modified_files_in_git_index = re_modified.findall(git_status)
      files = []
      for nb_file in modified_files_in_git_index:
          if nb_file.startswith('"') and nb_file.endswith('"'):
              nb_file = nb_file[1:-1]
          try:
              base_path(nb_file, fmt)
              files.append(nb_file)
          except InconsistentPath:
              continue
      return files
docs: Return the list of modified and deleted ipynb files in the git index that match the given format