“…This line of research has received much attention recently. Among others, they were investigated by [6,8,15,24,27,35,36,40] whose interest was focused on the estimation of the bivariate distribution of the gap times. In other cases, the interest was more focused on the distribution of the gap times, such as the estimation of the joint gap times, the gap time survival functions, or the conditional survival function of the gap times [20,21].…”