Farey map, Diophantine approximation and Bruhat-Tits tree
  Based on Broise-Alamichel and Paulin's work on the Gauss map corresponding to the principal convergents, we continue the study of the Gauss map via Farey maps to contain all the intermediate convergents. We define the geometric Farey map, which is given by time-1 map of the geodesic flow. We also define algebraic Farey maps, better suited for arithmetic properties, which produce all the intermediate convergents. Then we obtain the ergodic invariant measures for the Farey maps and the convergent speed. 
Dong Han Kim, Seonhee Lim, Hitoshi Nakada, Rie Natsui
math.DS math.GR math.NT