Limit cycles and center-focus of nonlinear systems
Two theorems are obtained for the nonlinear system \[ \dot x= h(y)- F(x),\quad \dot y= -g(x), \] to have \(n\) limit cycles (\(n\), any positive integer) or to have a center-focus (when \(n=+\infty\)), the conditions are too complicated to introduce here.
scientific article; zbMATH DE number 1286280