The function computes the estimate of the covariance of the test statistics of the test proposed by Zhao, Zhao, Sun, and Kim (2008).
It is not to be called by the user.
Qiang Zhao and Jianguo Sun
X. Zhao, Q. Zhao, J. Sun, Q. and J. S. Kim (2008), "Generalized Log-rank Tests for Partly Interval-Censored Failure Time Data", Biometrical Journal, 50 (3): 375-385.