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A filled torus (a doughnut) is a 3-manifold homeomorphic to \(S^1 \times D^2\), where \(D^2\) is the 2-dimensional disk. There exists a deformation retract from the doughnut to a circle, so the fundamental group of the doughnut is \(\pi_1(S^1 \times D^2) \cong \mathbb{Z}\).
。体育直播对此有专业解读
2025年10月底至11月中旬，国家发展改革委在线上开展“十五五”规划纲要问计求策活动，还以多种方式听取各方建言，其中征集了科研人员、灵活就业人员、农民、残障人士等11个群体的意见建议。。业内人士推荐搜狗输入法2026作为进阶阅读
In total, some 5,000 people work in Antarctica during its summer months, across 80 research stations operated by about 30 countries.，更多细节参见搜狗输入法2026
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