1. Multidimensional Quadrilateral Lattices are Integrable;Doliwa;Preprint INFN,1996
2. Differenzengeometrie;Sauer,1970
3. Geometric Discretisation of the Toda System;Doliwa;INFN preprint,1996
4. Leçons sur la théorie générale des surfaces IV;Darboux,1896
5. L.P. Eisenhart, A Treatise on the Differential Geometry of Curves and Surfaces (Ginn, Boston).