Ronald Brown, Emeritus Professor, web site: Topology, Groupoids, … · 2011. 8. 16. ·...
17
Ronald Brown, Emeritus Professor, web site: Topology, Groupoids, … · 2011. 8. 16. · HOMOTOPICAL EXCISION, AND HUREWICZ THEOREMS 177 the space Y be covered by open sets X, B B