David A. Bell J. W. Guan Suk Kyoon Lee Generalized Union and Project Operations for Pooling Uncertain and Imprecise Information. 89-117 1996 18 Data Knowl. Eng. 2 db/journals/dke/dke18.html#BellGL96 http://dx.doi.org/10.1016/0169-023X(95)00029-R