ZUO, Zhan-fei and HUANG, Yi-min. Absolute normalized norms in R^2 and Heinz means constant. Topological Methods in Nonlinear Analysis. Online. 24 September 2022. Vol. 60, no. 2, pp. 475 - 490. [Accessed 22 July 2024]. DOI 10.12775/TMNA.2022.003.