On 2-antiparallel encounters on factors of the hyperbolic plane

In this paper, we consider the geodesic flow on factors of the hyperbolic plane. We prove that a periodic orbit including a 2-antiparallel encounter has a partner orbit. We construct the partner orbit and give an estimate for the action different between the orbit pair. Then we apply the result to reprove the accuracy of Sieber/Richter’s prediction in [Sieber and Richter, 2001].