Algebraic and geometric aspects of rational Γ-inner functions

The setG=def{(z+w,zw):|z|<1,|w|<1}⊂C2 has intriguing complex-geometric properties; it has a 3-parameter group of automorphisms, its distinguished boundary is a ruled surface homeomorphic to the Möbius band and it has a special subvariety which is the only complex geodesic of G that is invariant under all automorphisms. We exploit the geometry of G to develop an explicit and detailed structure theory for the rational maps from the unit disc to the closure Γ of G that map the boundary of the disc to the distinguished boundary of Γ.