11 12 ' 21 22 



[21a,b] 



D b = b' + b" ; D^b = - b' + b" 

 b 11 11 11 ° 12 12 12 



^o. = -'b' + b" + Ob (b' - b" ) 

 2l 21 21 11 22 22 



b^^ = b' + b" + ab (b' - b" ' 

 22 22 22 12^ 22 22' 



D^ = 1 + o(b' + b" ) 

 b ' 12 12 



(The absence of primes on b,, and b after o is correct.) 

 Or, 



V = a^^F + a^2^ ; 6 = a^^F + ^^^Q 



[22a,b] 



D a, , = b' + b" + 2o(b' b" + b' b" ) 

 a 11 22 22 12 22 22 12 



D a,^ = b' - b" 

 a 12 12 12 



Da =b' -b" +a[(b' +b")(b" -b") 

 a 21 21 21 ^^12 12^^ 21 21^ 



-(b- + b" )(b' - b" )] 

 11 11 22 22 



^a-22 = ^ll -^ ^11 



D = (b' + b" )(b' + b" : 

 a 11 11^^ 22 22 



-(^l2 - ^l2)(^21 - ^21^ 



25 



