1. Aguilar, M., Gitler, S., Prieto, C.: Algebraic Topology from a Homotopical Viewpoint. Springer, New York (2002)
2. I. Berstein., Ganea, T.: The category of a map and of a cohomology class. Fundam. Math. 50(2), 265–279 (1961)
3. Borsuk, K.: Drei Sätze über die n-dimensionale Euklidische Sphäre. Fundam. Math. 20, 177–190 (1933)
4. Bredon, G.: Introduction to Compact Transformation Groups. Academic Press, Bolyai Janos Matematikai Tarsulat (1976)
5. Cornea, O., Lupton, G., Oprea, J., Tanré, D.: ‘Lusternik-Schnirelmann Category’, Mathematical Surveys and Monographs, 103. American Mathematical Society, Providence, RI (2003)