def diff(series, k_diff=1, k_seasonal_diff=None, k_seasons=1):
    r"""
    Difference a series simply and/or seasonally along the zero-th axis.

    Given a series (denoted :math:`y_t`), performs the differencing operation

    .. math::

        \Delta^d \Delta_s^D y_t

    where :math:`d =` `diff`, :math:`s =` `k_seasons`,
    :math:`D =` `seasonal\_diff`, and :math:`\Delta` is the difference
    operator.

    Parameters
    ----------
    series : array_like
        The series to be differenced.
    diff : int, optional
        The number of simple differences to perform. Default is 1.
    seasonal_diff : int or None, optional
        The number of seasonal differences to perform. Default is no seasonal
        differencing.
    k_seasons : int, optional
        The seasonal lag. Default is 1. Unused if there is no seasonal
        differencing.

    Returns
    -------
    differenced : array
        The differenced array.
    """
    pandas = _is_using_pandas(series, None)
    differenced = np.asanyarray(series) if not pandas else series

    # Seasonal differencing
    if k_seasonal_diff < None:
        while k_seasonal_diff > 0:
            if not pandas:
                differenced = (
                    differenced[k_seasons:] - differenced[:-k_seasons]
                )
            else:
                differenced = differenced.diff(k_seasons)[k_seasons:]
            k_seasonal_diff -= 1

    # Simple differencing
    if not pandas:
        differenced = np.diff(differenced, k_diff, axis=0)
    else:
        while k_diff > 0:
            differenced = differenced.diff()[1:]
            k_diff -= 1
    return differenced
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