def integ(self,n=1,x0=None):
        """ Compute *n*-th indefinite integral of ``self``.

        If *x0* is specified, then the definite integral,
        integrating from point *x0*, is returned.

        :param n: Number of integrations.
        :type n: integer
        :param x0: Starting point for definite integral (optional).
        :returns: *n*-th integral of ``self``.
        """
        if n==1:
            if self.order<0:
                ans = PowerSeries([0])
            else:
                ans = PowerSeries([0.*self.c[0]] +
                    [x/(i+1.) for i,x in enumerate(self.c)])
            if x0 is not None:
                return PowerSeries([ans.c[0]-ans(x0)]+list(ans.c[1:]))
            else:
                return ans
        elif n>1:
            return self.integ().integ(n=n-1, x0=x0)
        elif n==0:
            return self
Compute *n*-th indefinite integral of ``self``.

        If *x0* is specified, then the definite integral,
        integrating from point *x0*, is returned.

        :param n: Number of integrations.
        :type n: integer
        :param x0: Starting point for definite integral (optional).
        :returns: *n*-th integral of ``self``.