1. Markov's Theorem and 100 Years of the Uniqueness Conjecture;Aigner,2015
2. A Course in Metric Geometry, vol. 33;Burago,2001
3. Approach to Markoff's minimal forms through modular functions;Cohn;Ann. Math.,1955
4. Lifting representations to covering groups;Culler;Adv. Math.,1986
5. The Markoff and Lagrange Spectra, vol. 30;Cusick,1989