Past exam of the mathematics course of the University of Cambridge 2018 iii Paper 141 1 c Solution Created 2026-10-03 Updated 2026-10-05
The elliptization theorem says that a closed oriented three-manifold with finite fundamental group has spherical geometry. When the fundamental group is a cyclic group, it is a lens space. Consequently the candidates are with , using the same surgery orientation convention throughout.
The oriented classification of lens spaces says that and are related by an orientation-preserving homeomorphism exactly when . Since , , and modulo five, the complete list isThese are three distinct oriented homeomorphism classes. Reversing orientation interchanges and ; the class containing and admits an orientation-reversing homeomorphism. The elliptization theorem and the stated oriented classification of lens spaces are the general classification results used here.