[1] Bo?in V, Lakic N, Markovi? V, et al. Unique extremality. Journal d'Analyse Mathématique, 1998, 75(1):299-338
[2] Gardiner F P. Teichmüller Theory and Quadratic Differentials. New York:John Wiley & Sons, 1987
[3] Gardiner F P, Lakic N. Quasiconformal Teichmüller Theory. Amer Math Soc, 2000
[4] Li Z, Qi Y. Fundamental inequalities of Reich-Strebel and triangles in a Teichmüller space. Contem Math, 2012, 575:283-297
[5] Reich E. On criteria for unique extremality of Teichmüller mappings. Ann Acad Sci Fenn Series A I Math, 1981, (6):289-301
[6] Reich E. The unique extremality counterexample. Journal d'Analyse Mathématique, 1998, 75(1):339-347
[7] Reich E, Strebel K. On quasiconformal mappings which keep the boundary points fixed. Trans Amer Math Soc, 1969:211-222
[8] Reich E, Strebel K. Extremal plane quasiconformal mappings with given boundary values. Bull Amer Math Soc, 1973, 79(2):488-490
[9] Strebel K. On quasiconformal mappings of open Riemann surfaces. Commentarii Mathematici Helvetici, 1978, 53(1):301-321