Generic singularities of the 3D-contact sub-Riemannian conjugate locus

Agrachev, 1995, Methods of control theory in nonholonomic geometry Agrachev, 1996, Exponential mappings for contact sub-Riemannian structures, J. Dyn. Control Syst., 2, 321, 10.1007/BF02269423 Agrachev, 1998, Subriemannian metrics on R3, Proc. Can. Math. Soc., 25, 29 Agrachev, 2000, On subriemannian caustics and wave fronts for contact distributions in the three space, J. Dyn. Control Syst., 6, 365, 10.1023/A:1009566723037 Agrachev, 2019, A Comprehensive Introduction to Sub-Riemannian Geometry, 10.1017/9781108677325 Chakir, 1996, Small sub-Riemannian balls on R3, J. Dyn. Control Syst., 2, 359, 10.1007/BF02269424 Hirsch, 1974, Differential Topology, vol. 33 Sacchelli