The number of limit cycles from the perturbation of a quadratic isochronous system with two switching lines

In this paper, we give an upper bound (for \begin{document}$ n\geq3 $\end{document}) and the least upper bound (for \begin{document}$ n = 1,2 $\end{document}) of the number of limit cycles bifurcated from period annuli of a quadratic isochronous system under the piecewise polynomial perturbations of degree \begin{document}$ n $\end{document}, respectively. The results improve the conclusions in [19].