error in Huang et al. 1998

Equations 6.3 and 6.4 in Huang et al. Proc.R.Soc.Lond. A, 454, 903 are in error. In the double summation j should run from k+1 to n+1. I suspect there should also be a 2 in front of the summation. Note of course that X^2(t) should be outside the parentheses.

Keywords: HHT, GW