<div style="padding:40px;color:#cbccc6"><h1>甜甜圈 ↔ 咖啡杯</h1><p>拓扑同胚：同 genus 物体。</p><div style="padding:20px;background:#0d1017;border-left:3px solid #ffb454"><span class="katex-display"><span class="katex"><span class="katex-html" aria-hidden="true"><span class="mspace newline"></span><span class="base"><span class="strut" style="height:0.8778em;vertical-align:-0.1944em;"></span><span class="mord mathnormal">t</span><span class="mord mathnormal">e</span><span class="mord mathnormal">x</span><span class="mord mathnormal">t</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.0359em;">g</span><span class="mord mathnormal">e</span><span class="mord mathnormal">n</span><span class="mord mathnormal">u</span><span class="mord mathnormal">s</span><span class="mord">1</span><span class="mord cjk_fallback">同胚</span></span></span></span></span></span></div><p style="color:#707a8c">该页面需要 JavaScript 进行交互式可视化。</p></div>