John Yen Generalizing the Dempster-Shafer Theory to Fuzzy Sets. 529-554 2008 Classic Works of the Dempster-Shafer Theory of Belief Functions http://dx.doi.org/10.1007/978-3-540-44792-4_21 series/sfsc/2008-219 db/series/sfsc/sfsc219.html#Yen08