Singh, R. P., and J. D. Bhardwaj. “ON AXIOMATIC CHARACTERISATION OF GENERALIZED QUALITATIVE MEASURE OF VARIATION OF INFORMATION THROUGH GENERATING FUNCTION”. Tamkang Journal of Mathematics, vol. 21, no. 4, Dec. 1990, pp. 365-76, doi:10.5556/j.tkjm.21.1990.4685.