Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2022/iii/paper-114/4/1/solution

Put and let . The restriction
is a homeomorphism. At every point of , transport the local orientation of through this homeomorphism. The localization of the global class is therefore a generator at one, and hence every, point of that connected open set. The localizations of a global homology class form a section of the orientation local system; because the manifold is connected, this generator extends across . Thus is a fundamental class for an orientation of .
Choose . By the degree of a map between oriented manifolds,
so .

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