code: def param_names(self):
          
          pn = CombinedBounds(self.k.param_names, self.noise_k.param_names)
          if self.mu is not None:
              pn = CombinedBounds(pn, self.mu.param_names)
          return pn
docs: Combined names for the hyperparameters for the kernel, noise kernel and (if present) mean function.