<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def extreme_temperature_range(tasmax, tasmin, freq='YS'):
 r"""Extreme intra-period temperature range. The maximum of max temperature (TXx) minus the minimum of min temperature (TNn) for the given time period. Parameters tasmax : xarray.DataArray Maximum daily temperature values [℃] or [K] tasmin : xarray.DataArray Minimum daily temperature values [℃] or [K] freq : str, optional Resampling frequency Returns ------- xarray.DataArray Extreme intra-period temperature range for the given time period. Notes ----- Let :math:`TX_{ij}` and :math:`TN_{ij}` be the daily maximum and minimum temperature at day :math:`i` of period :math:`j`. Then the extreme temperature range in period :math:`j` is: .. math:: ETR_j = max(TX_{ij}) - min(TN_{ij}) """


    tx_max = tasmax.resample(time=freq).max(dim='time')
    tn_min = tasmin.resample(time=freq).min(dim='time')

    out = tx_max - tn_min
    out.attrs['units'] = tasmax.units
    return out