1 f~3 



h dn (70) 



' " T «S < < 71 > 



where q h (£,n) = q n ( x >y) anc * ttie lower limit of integrals depends on the 

 origin of $ and ! F. If we assume q fl to be slowly varying, so that d q^/c 

 and 8 q n /9^ are 0(1), we can prove 





Differentiating again by £ and taking only the term of the lowest order, 

 we have 



d \ 1 .6 3 \ 

 ? 2 ^0 2 



(73) 



A similar assumption is applied to 3<j>../8t; such as 



°*1 1 .2 UT 1 , 7/ , 



IT = T q o *F (74) 



2 2 

 Multiplying q n /Y n on both sides of Equation (69) and writing 



D(x,y) = E(€,n) (75) 



we obtain 



30 



