Here, the second terms are of order t−2(pm + pn − pl) whereby pm + pn − pl = 1 + 2 |pl| > 1.Excepting the case (p1, p2, p3) = (0, 0, 1), in which the metric singularity is fictitious. To remove these terms and restore the metric , it is necessary to impose on the coordinate functions the condition λ = 0.
