A finitely presented infinite simple group of homeomorphisms of the circle

We construct a finitely presented, infinite, simple group that acts by homeomorphisms on the circle, but does not admit a non-trivial action by C1-diffeomorphisms on the circle. This is the first such example. The group emerges as a group of piecewise projective homeomorphisms of S1=R?{infinity}. We also show that it does not admit a non-trivial action by piecewise linear homeomorphisms of the circle. Another interesting and new feature of this example is that it produces a non-amenable orbit equivalence relation with respect to the Lebesgue measure.