[1] M. Belis, S. Guiaşu: A quantitative-qualitative measure of information in cybernetics. IEEE Trans. Inform. Theory IT-14 (1968), 593-594.
[2] J. Havrda, F. Charvát:
Quantification method of classification processes, concept of structural $\alpha$-entropy. Kybernetika 3 (1967), 1, 30-35.
MR 0209067