The universal cover of a connected closed manifold of dimension three with finite fundamental group is a closed simply connected three-manifold. It is orientable, since its orientation character has trivial domain. Its first integral homology vanishes, and the universal coefficient theorem for cohomology then gives . Integral Poincare duality gives , while and are . Thus it is an integral homology sphere. This proof does not require classifying simply connected three-manifolds.
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