code: def deriv2(self, p):
          
          return self.power * (self.power - 1) * np.power(p, self.power - 2)
docs: Second derivative of the power transform
  
          Parameters
          ----------
          p : array-like
              Mean parameters
  
          Returns
          --------
          g''(p) : array
              Second derivative of the power transform of `p`
  
          Notes
          -----
          g''(`p`) = `power` * (`power` - 1) * `p`**(`power` - 2)