Yevstafyeva , V. V. “Existence of Two-Point Oscillatory Solutions of a Relay Nonautonomous System With a Multiple Eigenvalue of a Real Symmetric Matrix”. Ukrains’kyi Matematychnyi Zhurnal 73, no. 5 (May 24, 2021): 640–650. Accessed April 11, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/6379.