The definition of a D-number is given by Y. Deng in his paper, " D-numbers: Theory and Applications" published in the Journal of Information & Computational Science 9: 9 (2012), pp. 2421-2428 is perhaps not correct.
Let us look at the definition:
Let Omega be a finite nonempty set, D number is a mapping D from Omega to [0, 1] such that
Sum of (D(B): B is a subset of Omega} is Less than or equal to 1.
By its definition D has the domain Omega. So, D is applicable to elements of Omega. How it is applied to subsets of Omega?
Should we replace the definition as D is a mapping from P(Omega) to [0, 1]?