For s_1, s_2 = ± 1, lim_(ϵ_1->0 ϵ_2->0) 1/(x_1 - i s_1 ϵ_1) 1/(x_2 - i s_2 ϵ_2) = [P V(1/x_1) + i π s_1 δ(x_1)][P V(1/x_2) + i π s_2 δ(x_2)] + π^2 δ(x_1) δ(x_2), where δ(x) is the delta function and P V denotes the Cauchy principal value.