Subzone [I] is divided into four regions: 
G) b, <0,b)>0 
@) b; <0,b2 <0 
GB) b; > 0,b2>0 
) b1 > 0,b2 <0 
as shown in Fig. 5.31, just similar to Fig. 5.16. 
Fig. 5.31. Invertible Subzones [1] and [II]; @). @), ©), ® for by, bo. 
Xx; =€,;+ by €,1+ b2 € 12 
Xp = Ep-r + D1 € p71 + 52 € 1-7-2. 
Therefore, multiplying both sides of these two equations respectively and taking the ex- 
pected values of each term, 
E[X, -X,+] = Ele, €:-7]+ bf El€et- €r-+-1)+ 3 El€s2€++2] 
+ by{ Ela evr] + Eley: €x1-1]} + bo Ele 2 €ne] + Els: €nr-2)} 
+ bib2|E leet: €rr-2) + Elna €rr-1]}. 
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