The discontinuous matching of two planar linear foci can have three nested crossing limit cycles (Q482174)

Planar piecewise linear systems with two zones and a discontinuity line have been largely studied. In particular, to determine their maximum number of crossing limit cycles is an open question. In [\textit{S.-M. Huan} and \textit{X.-S. Yang}, Discrete Contin. Dyn. Syst. 32, No. 6, 2147--2164 (2012; Zbl 1248.34033)], there is presented an example with numerical evidences of the existence of three crossing limit cycles. In the reviewed paper, the authors prove following a bifurcation approach the existence of examples with three crossing limit cycles. In their examples both linear systems are of focus type.