Understand The Baire Category Theorem: Dense Sets, Nowhere Dense Sets, & Infinity

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Need help understanding dense sets, nowhere dense sets, and the Baire Category Theorem? Want another way to prove that the real number are uncountable? Here's a detailed treatment of these topics. Thanks for watching, check out the rest of the playlist!
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So far the most intuitive explanation of the concept of nowhere dense sets that I saw on the internet. Thank you for making this video!

shramini
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Incredible explanation. Thanks so much!!!

jakegameroff
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I see. You’re right that I’m not using the definition in 2:05. Instead I’m showing an equivalent statement that R/Z is a dense open subset of R.

DrMcCrady
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In 8:40 you say we're allowed to take that radius r_1 such that 0<r_1<1. Is it so because as B(x, r) \cap U_1 is open then we can find a radius l>0 where B(y_1, l) is contained in B(x, r) \cap U_1 but if we take a real number r_1 such that 0<r_1<min(1, L) small enough (the density of the rationals or the Archimedean property can help us control its smallness) such that the closure of B(y_1, r_1) (the ball itself with the point z in X such that d(z, y_1) = r_1 ) is contained in B(x, r) \cap U_1? And is it the same reasoning for 9:26, right?

jeanveramorocho
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2: 15 I do not understand how the example is tied to the definition. Why do we take x outside Z ? Based on the definition, shouldn't we take x from the closure of Z which is Z again??

Tatiana-zsdc