But it is not so, here we give an example to show that even if AB and BA are of
same order they may not be same Example 14 If 
1
0
A
0
1


= 
−


 and 
0
1
B
1
0


= 



, then 
0
1
AB
1
0


= 

−
 and
0
1
BA
1
−0


= 


 Clearly AB ≠ BA