1. Elements of modern topology;Brown,1968
2. Brown, R. and P. J. Higgins — On the connection between the second relative homotopy groups of some related spaces (submitted).
3. Double groupoids and crossed modules;Brown;Cah. de Top. Géom. Diff.,1976
4. Brown, R. and C. B. Spencer — A homotopy notion for double groupoids, in preparation.
5. On the homomorphisms of sequences;Cockcroft,1952