code: def deriv(self, p):
          
          p = self._clean(p)
          return 1. / self.dbn.pdf(self.dbn.ppf(p))
docs: Derivative of CDF link
  
          Parameters
          ----------
          p : array-like
              mean parameters
  
          Returns
          -------
          g'(p) : array
              The derivative of CDF transform at `p`
  
          Notes
          -----
          g'(`p`) = 1./ `dbn`.pdf(`dbn`.ppf(`p`))