Dulac's Problem and of the Focus Center on Two-Dimensional Manifolds
Bifurcation of limit cycles in smooth piecewise systems and an application in Medi...
On limit cycles that bifurcates from a center in a planar polynomial system.
Bifurcation of Limit Cycles from Polycycles in Dynamical Systems
Limit cycles, regularization and period function of piecewise smooth planar systems.