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www.logicmatters.net
| | neilmadden.blog
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| | I saw another article on Gödel's incompleteness theorems linked from Reddit today. It's a topic I've wanted to write about for some time. Although many articles do a decent job in giving an idea of what the big deal is (and this one is pretty good), they can sometimes give a misleading impression of what...
| | www.umsu.de
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| | xorshammer.com
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| | Let $latex \mathrm{PA}$ be Peano Arithmetic. Gödel's Second Incompleteness Theorem says that no consistent theory $latex T$ extending $latex \mathrm{PA}$ can prove its own consistency. (I'll write $latex \mathrm{Con}(T)$ for the statement asserting $latex T$'s consistency; more on this later.) In particular, $latex \mathrm{PA} + \mathrm{Con}(\mathrm{PA})$ is stronger than $latex \mathrm{PA}$. But certainly, given that...
| | dominiczypen.wordpress.com
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| Let $latex \omega$ denote the first infinite cardinal - that is, the set of non-negative integers. Let $latex p_0 = 2$ be the smallest prime number, and let $latex (p_n)_{n\in\omega}$ enumerate all prime numbers in ascending order. Let $latex \mathcal{U}$ be a free ultrafilter on $latex \omega$. We consider the field $latex F = \big(\prod_{n\in\omega}\mathbb{Z}/p_n\mathbb{Z}\big)/{\mathcal...