Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2019/ii/paper-4/21f/solution

For a continuous self-map of a finite CW complex, its Lefschetz number over is
The Lefschetz fixed-point theorem states that implies that has a fixed point. Consequently every fixed-point-free self-map has Lefschetz number zero.
The space in the question is a cyclic point-gluing of two-spheres. Before gluing, the spheres have total Euler characteristic . Each of the point identifications lowers the Euler characteristic by one, so
Equivalently, , with rational homology dimensions in degrees zero, one, and two.

New to topics? Read the docs here!