code: def plot_decorate_rebits(basis=None, rebit_axes=REBIT_AXES):
      
      ax = plt.gca()
  
      if basis is not None:
          labels = list(map(r'$\langle\!\langle {} | \rho \rangle\!\rangle$'.format,
              # Pick out the x and z by default.
              [basis.labels[rebit_axes[0]], basis.labels[rebit_axes[1]]]
          ))
          plt.xlabel(labels[0])
          plt.ylabel(labels[1])
  
      ax.add_artist(plt.Circle([0, 0], 1, color='k', fill=False))
      ax.set_xlim(-1.1, 1.1)
      ax.set_ylim(-1.1, 1.1)
      ax.set_aspect('equal')
docs: Decorates a figure with the boundary of rebit state space
      and basis labels drawn from a :ref:`~qinfer.tomography.TomographyBasis`.
  
      :param qinfer.tomography.TomographyBasis basis: Basis to use in
          labeling axes.
      :param list rebit_axes: List containing indices for the :math:`x`
          and :math:`z` axes.