“…In the limit of ρ → 0 we have < I 1,1 + I 1,3 + I 10,1 + I 10,3 > = 0 (Ia), < I 5,1 + I 5,3 + I 6,1 + I 6,3 > = 0 (Ib), < I 2,1 + I 2,3 + I 9,1 + I 9,3 > = 0 (IIa), 12 A different proof may be obtained by isolating the singularity at u = 0 in appropriate functions f 2 or f 4 . At these points, the paired integrands match and cancel out.…”