Equation Icon  [h1, h2] = 0, [h1,e1] = 2e1, [h1,e2] = − e2, [h1,f1] = − 2f1, [h1,f2] = f2, [h2,e1] = − e1, [h2,e2] = 2e2, [h2,f1] = f1, [h2,f2] = − 2f2, (4.20) [e1,[e1,e2]] = 0, [e2,[e2,e1]] = 0, [f1,[f1,f2]] = 0, [f2,[f2,f1]] = 0 [ei,fj] = δijhj.