Кузьменко, А.Г. 2014. “An Universal Law of Periodicity of Catastrophes Is in the Heterogeneous Nonlinear Dynamic Systems. Part 1. Theorem about Periodicity of Catastrophes”. Problems of Tribology 65 (3):101-5. https://tribology.khnu.km.ua/index.php/ProbTrib/article/view/256.