The minimum mean square estimator for a sublinear operator
  In this paper, we study the minimum mean square estimator for a sublinear operator. Under some mild assumptions, we prove the existence and uniqueness of the minimum mean square estimator. Several characterizations of the minimum mean square estimator are obtained. We also explore the relationship between the minimum mean square estimator and the conditional coherent risk measure and conditional g-expectation. 
Ji Shaolin, Sun Chuanfeng
math.PR