“…Under certain conditions, the optimal solution from this perspective is closely related to nonparametric empirical Bayes estimators (Brown and Greenshtein, 2009;Jiang et al, 2009;Zhang, 2003 (Castillo et al, 2012;Johnstone, 1994, 1995;Martin et al, 2014). Heteroscedastic normal sequences, where the X i1 can have different variances for different indices i, have also been considered, both when the variances are known (Fu et al, 2019;Tan, 2016;Weinstein et al, 2018;Xie et al, 2012;Zhang and Bhattacharya, 2017) and when they are unknown but estimates are available (Feng and Dicker, 2018;Gu and Koenker, 2017;Jing et al, 2016).…”