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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 tg_max(tas, freq='YS'):
 r"""Highest mean temperature. The maximum of daily mean temperature. Parameters tas : xarray.DataArray Mean daily temperature [℃] or [K] freq : str, optional Resampling frequency Returns ------- xarray.DataArray Maximum of daily minimum temperature. Notes ----- Let :math:`TN_{ij}` be the mean temperature at day :math:`i` of period :math:`j`. Then the maximum daily mean temperature for period :math:`j` is: .. math:: TNx_j = max(TN_{ij}) """


    return tas.resample(time=freq).max(dim='time', keep_attrs=True)