def METHOD_NAME(self):
    r"""
    Return the parameter set of this function derivative operator.
    This is the list of indices of variables with respect to which
    the derivative is taken.
    EXAMPLES::
        sage: from sage.symbolic.operators import FDerivativeOperator
        sage: f = function('foo')
        sage: op = FDerivativeOperator(f, [0, 1])
        sage: op.parameter_set()
        [0, 1]
    """
    return self._parameter_set