The function computes the estimate of the covariance of the test statistics of the test proposed by Sun, Zhao, and Zhao (2005).
It is not to be called by the user.
Qiang Zhao and Jianguo Sun
J. Sun, Q. Zhao, and X. Zhao (2005), "Generalized Log-rank Test for Interval-Censored Data", Scandinavian Journal of Statistics, 32: 45-57.