Weiyin Fei Rangquan Wu Shihuang Shao Doob's stopping theorem for fuzzy (super, sub) martingales with discrete time. 377-390 2003 135 Fuzzy Sets and Systems 3 http://www.sciencedirect.com/science/article/B6V05-45X2SR6-1/2/87f15cb2e3c264adf8b5359517254ff4 db/journals/fss/fss135.html#FeiWS03