def val_and_std(token):
    """check the validity of a token; standard it if needed
    Args:
        token (string): a token
    Returns:
        string: an standardized token if the token is valid
        otherwise return None
    """
    token = token.strip("\"\'-")
    tran_t = token.replace("-", "").replace("'", "")
    if tran_t.isascii() and tran_t.isalpha():
        return token.lower()
    return None