No. Its top nonzero group would force dimension three. Poincare duality requires , and the universal coefficient theorem gives , since is free. This contradicts the proposed vanishing of . Equivalently its listed Betti numbers give Euler characteristic , impossible for a closed oriented odd-dimensional manifold.
No. The dimension would again be three. The universal coefficient theorem gives , since both and vanish. Poincare duality then forces , contradicting the proposed torsion group. In general the second integral homology of a connected closed oriented three-manifold is free abelian, being dual to its first homology.
Universal coefficient theorem 2026-10-14
The universal coefficient theorem relates homology or cohomology with different coefficient groups through tensor and Tor, or Hom and Ext, respectively. The universal coefficient theorem for homology is its tensor-Tor sequence; the universal coefficient theorem for cohomology is its Hom-Ext sequence.
Universal coefficient theorem for cohomology Created 2026-09-24 Updated 2026-10-14
This is the cohomological form of the universal coefficient theorem, with Ext and Hom terms rather than the homological tensor and Tor terms.
Universal coefficient theorem for homology Created 2026-09-24 Updated 2026-10-14
For an abelian coefficient group , there is a split short exact sequenceFor , the Tor term vanishes.
This is the homology case of the universal coefficient theorem; its cohomology case uses Hom and Ext rather than tensor product and Tor.