In this talk the goal is to present new results and questions
on an old idea initially due to R.Bowen and C.Series. In their paper,
back to 1979, they defined a single map associated to a group. This
particular map satisfies some nice dynamical properties, relating the
dynamics with the group.
I will discuss new constructions and results based on this idea. The
groups in question are, unfortunately, limited to surface groups, i.e.
fundamental group of a surface.
The associated maps belong to a class that is not so studied: expanding piecewise homeomorphisms of the circle.
The questions go in both directions: group and dynamics and there are
many challenges that I will try to explain.