Quasi-periodic stability of subfamilies of an unfolded skew Hopf bifurcation (Q1570977)

The authors deal with the following question: Under what conditions does an invariant quasi-periodic circle persist in a skew Hopf bifurcation family? It turns out that an unfolding of the skew Hopf family has to be considered. In this case the invariant circle persists for subfamilies of that unfolding. To prove this fact the authors develop an extension of ordinary KAM theory.