1. On locally simply connected toposes and their fundamental groups;Barr;Cah. Top. Géom. Diff. Cat.,1981
2. Fibrations of groupoids;Brown;J. Algebra,1970
3. On the connection between the second relative homotopy groups of some related spaces;Brown,1978
4. Colimit theorems for relative homotopy groups;Brown;J. Pure Appl. Algebra,1981
5. Van Kampen theorems for diagrams of spaces;Brown;Topology,1987