As mathematicians say, “Every simply connected closed 3-manifold is homeomorphic to a 3-sphere.”

用数学语言表达就是“每个单连通3重（3-manifold）封闭体与一个三维球体同胚（homeomorphic）。”

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Also, the paper discuss the existence of the infinite closed geodesics of a compact no-simply connected Riemannian manifold.

并由此讨论了紧致的非单连通黎曼流形上无穷多的闭测地线存在性问题。

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As mathematicians say, "Every simply connected closed 3-manifold is homeomorphic to a 3-sphere."

用数学语言表达就是“每个单连通3重（3-manifold）封闭体与一个三维球体同胚（homeomorphic）。”

youdao