Ésik, Zoltán, Uli Fahrenberg, Axel Legay, and Karin Quaas. “An Algebraic Approach to Energy Problems II - the Algebra of Energy Functions”. Acta Cybernetica 23, no. 1 (January 1, 2017): 229-268. Accessed August 4, 2020. https://cyber.bibl.u-szeged.hu/index.php/actcybern/article/view/3924.