Zhang , Qing and Du , Zhengdong. (2024). An Example of Piecewise Linear Systems with Infinitely Many Limit Cycles Separated by a Piecewise Linear Curve and Its Perturbations.
            <i>Journal of Nonlinear Modeling and Analysis</i>. <i>6</i> (3).
            759-774.
         doi:10.12150/jnma.2024.759