and

 iJ = HijdA
 Jc

 = L-IJS K L 6IJKLMK L
 + 5 KP L K 1KP JK dA + (p4 /4)

 6IJSKL X 6IJSKLMXK XLXM
 3 12
 + 5IKpLPLXKX LxJ t IKPP JXK 2 + O(4/R4). (4-67)
 84 84

In terms of 'HAB, Synge's world function is expressed as [18]

 1 1 1
 7(p, p') ABrlAB + 1(7 _-)2YHo + (7 T')X HIO +IJ
 2 2 2
 +O(p6/R4)

 2 (1 Roo) [(r' 7 + X'H0o)2 _- IXJ(r + 'j)/(1 oo)]

 +O(p6/R4). (4-68)

 With the source point p' on F, the second term in the square brackets above
can be modified with the help of Eqs. (4-65) and (4-67),

 X'X(rqi, +'Huj) = p2( +' oo) + O(p6/R4), (4-69)

where

 p2 XI XJj. (4-70)

Substituting Eq. (4-69) into Eq. (4-68) and factorizing o, we obtain [18]

 S(p,p') 2(1 Roo) [- 7 + X'jo- p(1 + Hoo)]

 x [T' T + X'-Io + p(l + Hoo)] + O(p6/R4). (4-71)