Take a finitely-generated group of (analytic) circle diffeomorphisms. Since the times of Poincaré we know that any such action admits either a finite orbit, or a Cantor minimal set, or the action is minimal on all the circle. But what else can be said on such a group?

In this direction, there are well-known questions due to Sullivan, Ghys and Hector: assuming that such an action is minimal, is it necessarily Lebesgue-ergodic? If there is a Cantor minimal set, is it necessarily of a zero Lebesgue measure?

Our results provide a positive answer to the latter question, in some cases allow to resolve the former one and, more generally speaking, give some kind of understanding how a general characterization of an action can look like. This is a joint project with B. Deroin, D. Filimonov, and A. Navas.