Limit cycles bifurcating from an invisible fold-fold in planar piecewise Hamiltonian systems (Q2660559)

The paper deals with piecewise differential systems and the existence of limit cycles which bifurcates from an invisible fold-fold at the origin after some perturbation. The authors state three main results which give conditions for, given an integer \(k\), there exist exactly \(k\) hyperbolic crossing limit cycles in a suitable neighborhood of the origin. The theories of Lyapunov constants and piecewise differential systems are used to proof the results.