1. Hexagonal circle patterns and integrable systems: Patterns with constant angles,;A. Bobenko;Duke Math. J.,2003
2. "Discrete Differential Geometry. Integrable Structure,";A. Bobenko;Amer. Math. Soc.,2008
3. "Projective geometry and projective metrics,";H. Busemann;Academic Press,1953
4. Integrable systems. I,;B. Dubrovin;in,2001
5. "Hamiltonian Methods in the Theory of Solitons,";L. Faddeev;Springer-Verlag,1987