Nohara BT. Nonexistence theorem except the out-of-phase and in-phase solutions in the coupled van der Pol equation system. Ukr. Mat. Zhurn. [Internet]. 2009Aug.25 [cited 2024Nov.22];61(8):1106-29. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/3084