where the power set formula_4 contains all possible subsets of the frame of discernment formula_5. In contrast to the DST the mass formula_6 allocated to the empty set formula_7 is not required to be zero, and hence generally formula_8 holds true. The underlying idea is that the frame of discernment is not necessarily exhaustive, and thus belief allocated to a proposition formula_9, is in fact allocated to formula_10 where formula_11 is the set of unknown outcomes. Consequently, the combination rule underlying the TBM corresponds to Dempster's rule of combination, except the normalization that grants formula_12. Hence, in the TBM any two independent functions formula_13 and formula_14 are combined to a single function formula_15 by: