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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def tn_days_below(tasmin, thresh='-10.0 degC', freq='YS'):
 r"""Number of days with tmin below a threshold in Number of days where daily minimum temperature is below a threshold. Parameters tasmin : xarray.DataArray Minimum daily temperature [℃] or [K] thresh : str Threshold temperature on which to base evaluation [℃] or [K] . Default: '-10 degC'. freq : str, optional Resampling frequency Returns ------- xarray.DataArray Number of days Tmin < threshold. Notes ----- Let :math:`TN_{ij}` be the daily minimum temperature at day :math:`i` of period :math:`j`. Then counted is the number of days where: .. math:: TX_{ij} < Threshold [℃] """

    thresh = utils.convert_units_to(thresh, tasmin)
    f1 = utils.threshold_count(tasmin, '<', thresh, freq)
    return f1