docs: def _smooth_interpolated_smooth(self):
          """
          Smooth interpolated results with tweeter span.
  
          A final step of the supersmoother is to smooth the interpolated values with
          the tweeter span. This is done in Breiman's supsmu.f but is not explicitly
          discussed in the publication. This step is necessary to match
          the FORTRAN version perfectly.
          """
          smoothed_results = smoother.perform_smooth(self.x,
                                                     self.smooth_result,
                                                     TWEETER_SPAN)
          self.smooth_result = smoothed_results.smooth_result