1. V.I. Arnold, Invarianty i perestroiki ploskih frontov, Trudy Mat. Inst. Steklov. 209 (1995);
2. English translation: Invariants and perestroikas of wave fronts on the plane, Singularities of smooth mappings with additional structures, Proc. Steklov Inst. Math. 209 (1995) 11–64.
3. Quantization of the algebra of chord diagrams;Andersen;Math. Proc. Cambridge Philos. Soc.,1998
4. Über systemevon linearen partiellen differentialgleichungen erster ordnung;Chow;Math. Ann.,1939
5. Riemannian Geometry;do Carmo,1992