C. Alonso-González, M. I. Camacho, and F. Cano. Topological invariants for singularities of real vector fields in dimension three. Discrete and Continuous Dynamical Systems. Series A, 20 4 (2008) 823-847.
C. Alonso-González, M. I. Camacho, and F. Cano. Topological invariants for singularities of real vector fields in dimension three. Discrete and Continuous Dynamical Systems. Series A, 20 4 (2008) 823-847.