docs: def Jzjmcoeff(ls, m, shift) -> sympy.Expr:
      r'''Eigenvalue of the $\Op{J}_z$ (:class:`Jz`) operator
  
      .. math::
  
          \Op{J}_{z} \ket{s, m} = m \ket{s, m}
  
      See also :func:`Jpjmcoeff`.
      '''
      assert isinstance(ls, SpinSpace)
      n = ls.dimension
      s = sympify(n - 1) / 2
      assert n == int(2 * s + 1)
      if isinstance(m, str):
          return ls.basis.index(m) - s
      elif isinstance(m, int):
          if shift:
              assert 0 <= m < n
              return m - s
      else:
          return sympify(m)