def read_relative_operator_basenames(task):
    """ Read list of relative operators basenames.

    Returns:
        (list) : list of relative operators basenames
    """

    relative_operator_filename = "relative_operators.dat"

    # read list of unit tensors
    relative_operator_stream = open(relative_operator_filename,mode="rt")
    relative_operator_basename_list = [
        ## line.strip()  # remove trailing newline
        (line.split())[0]  # basename is leading element on line
        for line in relative_operator_stream
    ]
    relative_operator_stream.close()
    return relative_operator_basename_list