i found it, i found it :-))))) >A particular favorite of mine: > >a=b=1 >a**2=ab >a**2-b**2=ab-b**2 >(a+b)(a-b)= b(a-b) right, you can not devide by (a-b) since (1-1) = 0 >(a+b)=b >1+1=1 > >John