b=&-[a,e]e =a-a1          − −          − = 1 2 1 6 4 1 3 1          − = 1 1 1 3 5          − = = 1 1 1 3 1 2 2 2 b b e b e e 2 2 2 1 1 = −   ,  1 1 2 2 1 1 , b b b b     = −       2 1 1  2 2 1 ,b b b  = − 