Past exam of the mathematics course of the University of Cambridge 2009 iii Paper 16 1 3 Solution 2026-10-14
The space is the mapping torus of the antipodal map . For , its mapping degree is : is the restriction of on , whose determinant is . The Wang sequence givesThe kernel terms are free abelian, so these short exact sequences split as groups. On the map is the identity, and on it is multiplication by . For this givesAt , both contributions to degree one are present, giving and , with all other groups zero. At , the antipodal map exchanges the two points of , and the two cylinder intervals join into a single circle; thus and higher groups vanish. These are the homology of the antipodal sphere mapping torus cases.