Упражнение: докажите, что любую поверхность (компактную связную без края) можно получить из сферы последовательностью раздутий и сдутий.
«Топологическая гипотеза Нэша», доказанная Г.Михалкиным: аналогичное утверждение верно в любой размерности — любое вещественное многообразие (гладкое компактное связное без края) можно превратить в любое другое последовательностью раздутий и сдутий вдоль подмногообразий.
Упражнение: докажите, что любую поверхность (компактную связную без края) можно получить из сферы последовательностью раздутий и сдутий.
«Топологическая гипотеза Нэша», доказанная Г.Михалкиным: аналогичное утверждение верно в любой размерности — любое вещественное многообразие (гладкое компактное связное без края) можно превратить в любое другое последовательностью раздутий и сдутий вдоль подмногообразий.
// via ppetya
BY Непрерывное математическое образование
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Just days after Russia invaded Ukraine, Durov wrote that Telegram was "increasingly becoming a source of unverified information," and he worried about the app being used to "incite ethnic hatred." Telegram boasts 500 million users, who share information individually and in groups in relative security. But Telegram's use as a one-way broadcast channel — which followers can join but not reply to — means content from inauthentic accounts can easily reach large, captive and eager audiences. You may recall that, back when Facebook started changing WhatsApp’s terms of service, a number of news outlets reported on, and even recommended, switching to Telegram. Pavel Durov even said that users should delete WhatsApp “unless you are cool with all of your photos and messages becoming public one day.” But Telegram can’t be described as a more-secure version of WhatsApp. Update March 8, 2022: EFF has clarified that Channels and Groups are not fully encrypted, end-to-end, updated our post to link to Telegram’s FAQ for Cloud and Secret chats, updated to clarify that auto-delete is available for group and channel admins, and added some additional links. One thing that Telegram now offers to all users is the ability to “disappear” messages or set remote deletion deadlines. That enables users to have much more control over how long people can access what you’re sending them. Given that Russian law enforcement officials are reportedly (via Insider) stopping people in the street and demanding to read their text messages, this could be vital to protect individuals from reprisals.
from ms
