Definition 3 A universal cover of a topological space \(X\) is a covering space \(\tilde{X}\) of \(X\) that is simply connected, meaning that it has no nontrivial loops. The universal cover is unique up to homeomorphism and serves as a “universal” object in the category of covering spaces of \(X\).
Billy Crudup, The Morning Show
，这一点在体育直播中也有详细论述
图片来自《UI Design and Interaction Guide for Windows Phone 7 Series》动态磁贴也是同样的思路。它本质上是在尝试让用户不必打开应用，就能在开始屏幕上看到天气、日程或未读消息。这种理念比后来流行的通知中心和小组件还要更早一步。但受限于后台机制和开发者投入，磁贴往往更新不及时、可定制程度也有限，很多应用最终只是把它当成会动的图标。可以说是理念超前，却没能完全落地。
Сайт Роскомнадзора атаковали18:00