1. N. Aronszajn, Subcartesian and subriemannian spaces, Notices Amer. Math. Soc. 14 (1967), 111.
2. N. Aronszajn and P. Szeptycki, Subcartesian spaces, J. Diff. Geom. 15 (1980), 393–416.
3. L. Bates and E. Lerman, Proper group actions and symplectic stratified spaces, Pac. J. Math. 181 (1997), 201–229.
4. E. Bierstone, The Structure of Orbit Spaces and the Singularities of Equivariant Mappings, Monografias de Matemática35 Instituto de Matemática Pura e Aplicada, Rio de Janeiro, 1980.
5. M. Goresky and R. MacPherson, Intersection Homology Theory, Topology 19 (1980), 135–162.