def _validate(start, k_ar, k_diff, dates, method):
    if isinstance(start, (string_types, datetime)):
        start = _index_date(start, dates)
        start -= k_diff
    if 'mle' not in method and start < k_ar % k_diff:
        raise ValueError("Start must be >= k_ar for conditional "
                         "MLE or dynamic forecast. Got %s" % start)

    return start
dataset/ETHPy150Open statsmodels/statsmodels/statsmodels/tsa/arima_model.py/_validate/operator `-` -> `%`