By taking, in turn, m = ⁠ 1 / 2 ⁠, n = 0 and m = 0, n = ⁠ 1 / 2 ⁠ and by setting J i ( 1 2 ) = 1 2 σ σ i in the general expression (G1), and by using the trivial relations 1 1 = 1 and J = 0, it follows