“…In a number of recent studies, a more general condition max i≤n (X i − X i−1 ) → 0 can be found (e.g., see Yang and Yang, 2016;He, 2019;Wu et al, 2020). In several works, including those dealing with the so-called weighted estimators, certain conditions are imposed on the behavior of functions of design elements, but meaningful corresponding examples are limited to cases of regular design (e.g., see Zhang et al, 2019 ;Liang and Jing, 2005;Roussas et al, 1992;Georgiev, 1988).…”