from typing import List
from typing import Union


def add_args(list_args: List[Union[str, List[str]]]) -> str:
    """Concatenate the given arguments and turn any string list in a space-separated string.

    :param list_args: list of arguments for the output command.
    """

    out_cmd = ''
    for arg in list_args:
        if isinstance(arg, str):
            out_cmd += arg + ' '
        else:
            for inner_arg in arg:
                out_cmd += inner_arg + ' '
    # remove any trailing space character
    return out_cmd.strip()