Subgroups generated by two Dehn twists on a nonorientable surface
arXiv:1310.3033
Abstract
Let a and b be two simple closed curves on an orientable surface S such that their geometric intersection number is greater than 1. It is known that the group generated by corresponding Dehn twists t_a and t_b is isomorphic to the free group of rank 2. In this paper we extend this result to the case of a nonorientable surface.
This version incorporates the referee's suggestions. To appear in Topology Proceedings