Anthony Berg 8d6036292d
All checks were successful
/ Deploy to Cloudflare Pages (push) Successful in 1m9s
Quartz sync: Mar 1, 2025, 5:05 PM
2025-03-01 17:05:33 +01:00

74 lines
56 KiB
HTML
Raw Blame History

This file contains invisible Unicode characters

This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

<!DOCTYPE html>
<html lang="en"><head><title>Topology</title><meta charset="utf-8"/><link rel="preconnect" href="https://fonts.googleapis.com"/><link rel="preconnect" href="https://fonts.gstatic.com"/><link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=IBM Plex Mono&amp;family=Schibsted Grotesk:wght@400;700&amp;family=Source Sans Pro:ital,wght@0,400;0,600;1,400;1,600&amp;display=swap"/><link rel="preconnect" href="https://cdnjs.cloudflare.com" crossorigin="anonymous"/><meta name="viewport" content="width=device-width, initial-scale=1.0"/><meta name="og:site_name" content="ACIT4330 Lecture Notes"/><meta property="og:title" content="Topology"/><meta property="og:type" content="website"/><meta name="twitter:card" content="summary_large_image"/><meta name="twitter:title" content="Topology"/><meta name="twitter:description" content="Definition A collection of subsets of X, called open sets, such that: X, \, \emptyset \in \tau Any union of sets from \tau will be in \tau. Info y, z \in \tau \implies y \cup z \in \tau x_{i} \in \tau \implies \cup_{i \in I} X_{i} \in \tau Any finite intersection of sets from \tau will be in \tau."/><meta property="og:description" content="Definition A collection of subsets of X, called open sets, such that: X, \, \emptyset \in \tau Any union of sets from \tau will be in \tau. Info y, z \in \tau \implies y \cup z \in \tau x_{i} \in \tau \implies \cup_{i \in I} X_{i} \in \tau Any finite intersection of sets from \tau will be in \tau."/><meta property="og:image:type" content="image/webp"/><meta property="og:image:alt" content="Definition A collection of subsets of X, called open sets, such that: X, \, \emptyset \in \tau Any union of sets from \tau will be in \tau. Info y, z \in \tau \implies y \cup z \in \tau x_{i} \in \tau \implies \cup_{i \in I} X_{i} \in \tau Any finite intersection of sets from \tau will be in \tau."/><meta property="og:image:width" content="1200"/><meta property="og:image:height" content="630"/><meta property="og:image:url" content="https://https://acit4330.pages.anthonyberg.io//static/og-image.png"/><meta name="twitter:image" content="https://https://acit4330.pages.anthonyberg.io//static/og-image.png"/><meta property="og:image" content="https://https://acit4330.pages.anthonyberg.io//static/og-image.png"/><meta property="twitter:domain" content="https://acit4330.pages.anthonyberg.io/"/><meta property="og:url" content="https://https//acit4330.pages.anthonyberg.io/Definitions/Topological-Spaces/Topology"/><meta property="twitter:url" content="https://https//acit4330.pages.anthonyberg.io/Definitions/Topological-Spaces/Topology"/><link rel="icon" href="../../static/icon.png"/><meta name="description" content="Definition A collection of subsets of X, called open sets, such that: X, \, \emptyset \in \tau Any union of sets from \tau will be in \tau. Info y, z \in \tau \implies y \cup z \in \tau x_{i} \in \tau \implies \cup_{i \in I} X_{i} \in \tau Any finite intersection of sets from \tau will be in \tau."/><meta name="generator" content="Quartz"/><link href="../../index.css" rel="stylesheet" type="text/css" spa-preserve/><link href="https://cdn.jsdelivr.net/npm/katex@0.16.11/dist/katex.min.css" rel="stylesheet" type="text/css" spa-preserve/><script src="../../prescript.js" type="application/javascript" spa-preserve></script><script type="application/javascript" spa-preserve>const fetchData = fetch("../../static/contentIndex.json").then(data => data.json())</script></head><body data-slug="Definitions/Topological-Spaces/Topology"><div id="quartz-root" class="page"><div id="quartz-body"><div class="left sidebar"><h2 class="page-title"><a href="../..">ACIT4330 Lecture Notes</a></h2><div class="spacer mobile-only"></div><div class="search"><button class="search-button" id="search-button"><p>Search</p><svg role="img" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 19.9 19.7"><title>Search</title><g class="search-path" fill="none"><path stroke-linecap="square" d="M18.5 18.3l-5.4-5.4"></path><circle cx="8" cy="8" r="7"></circle></g></svg></button><div id="search-container"><div id="search-space"><input autocomplete="off" id="search-bar" name="search" type="text" aria-label="Search for something" placeholder="Search for something"/><div id="search-layout" data-preview="true"></div></div></div></div><button class="darkmode" id="darkmode"><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1" id="dayIcon" x="0px" y="0px" viewBox="0 0 35 35" style="enable-background:new 0 0 35 35" xml:space="preserve" aria-label="Dark mode"><title>Dark mode</title><path d="M6,17.5C6,16.672,5.328,16,4.5,16h-3C0.672,16,0,16.672,0,17.5 S0.672,19,1.5,19h3C5.328,19,6,18.328,6,17.5z M7.5,26c-0.414,0-0.789,0.168-1.061,0.439l-2,2C4.168,28.711,4,29.086,4,29.5 C4,30.328,4.671,31,5.5,31c0.414,0,0.789-0.168,1.06-0.44l2-2C8.832,28.289,9,27.914,9,27.5C9,26.672,8.329,26,7.5,26z M17.5,6 C18.329,6,19,5.328,19,4.5v-3C19,0.672,18.329,0,17.5,0S16,0.672,16,1.5v3C16,5.328,16.671,6,17.5,6z M27.5,9 c0.414,0,0.789-0.168,1.06-0.439l2-2C30.832,6.289,31,5.914,31,5.5C31,4.672,30.329,4,29.5,4c-0.414,0-0.789,0.168-1.061,0.44 l-2,2C26.168,6.711,26,7.086,26,7.5C26,8.328,26.671,9,27.5,9z M6.439,8.561C6.711,8.832,7.086,9,7.5,9C8.328,9,9,8.328,9,7.5 c0-0.414-0.168-0.789-0.439-1.061l-2-2C6.289,4.168,5.914,4,5.5,4C4.672,4,4,4.672,4,5.5c0,0.414,0.168,0.789,0.439,1.06 L6.439,8.561z M33.5,16h-3c-0.828,0-1.5,0.672-1.5,1.5s0.672,1.5,1.5,1.5h3c0.828,0,1.5-0.672,1.5-1.5S34.328,16,33.5,16z M28.561,26.439C28.289,26.168,27.914,26,27.5,26c-0.828,0-1.5,0.672-1.5,1.5c0,0.414,0.168,0.789,0.439,1.06l2,2 C28.711,30.832,29.086,31,29.5,31c0.828,0,1.5-0.672,1.5-1.5c0-0.414-0.168-0.789-0.439-1.061L28.561,26.439z M17.5,29 c-0.829,0-1.5,0.672-1.5,1.5v3c0,0.828,0.671,1.5,1.5,1.5s1.5-0.672,1.5-1.5v-3C19,29.672,18.329,29,17.5,29z M17.5,7 C11.71,7,7,11.71,7,17.5S11.71,28,17.5,28S28,23.29,28,17.5S23.29,7,17.5,7z M17.5,25c-4.136,0-7.5-3.364-7.5-7.5 c0-4.136,3.364-7.5,7.5-7.5c4.136,0,7.5,3.364,7.5,7.5C25,21.636,21.636,25,17.5,25z"></path></svg><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1" id="nightIcon" x="0px" y="0px" viewBox="0 0 100 100" style="enable-background:new 0 0 100 100" xml:space="preserve" aria-label="Light mode"><title>Light mode</title><path d="M96.76,66.458c-0.853-0.852-2.15-1.064-3.23-0.534c-6.063,2.991-12.858,4.571-19.655,4.571 C62.022,70.495,50.88,65.88,42.5,57.5C29.043,44.043,25.658,23.536,34.076,6.47c0.532-1.08,0.318-2.379-0.534-3.23 c-0.851-0.852-2.15-1.064-3.23-0.534c-4.918,2.427-9.375,5.619-13.246,9.491c-9.447,9.447-14.65,22.008-14.65,35.369 c0,13.36,5.203,25.921,14.65,35.368s22.008,14.65,35.368,14.65c13.361,0,25.921-5.203,35.369-14.65 c3.872-3.871,7.064-8.328,9.491-13.246C97.826,68.608,97.611,67.309,96.76,66.458z"></path></svg></button><div class="explorer"><button type="button" id="mobile-explorer" class="collapsed hide-until-loaded" data-behavior="collapse" data-collapsed="collapsed" data-savestate="true" data-tree="[{&quot;path&quot;:&quot;Definitions&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Functions&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Measure-Theory&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Measure-Theory/Sigma-Algebra&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Metric-Spaces&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Sets&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Statements&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Terminology&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Topological-Spaces&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Topological-Spaces/Induced&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Topological-Spaces/Terminologies&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Vector-Spaces&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Lectures&quot;,&quot;collapsed&quot;:true}]" data-mobile="true" aria-controls="explorer-content" aria-expanded="false"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="lucide lucide-menu"><line x1="4" x2="20" y1="12" y2="12"></line><line x1="4" x2="20" y1="6" y2="6"></line><line x1="4" x2="20" y1="18" y2="18"></line></svg></button><button type="button" id="desktop-explorer" class="title-button" data-behavior="collapse" data-collapsed="collapsed" data-savestate="true" data-tree="[{&quot;path&quot;:&quot;Definitions&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Functions&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Measure-Theory&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Measure-Theory/Sigma-Algebra&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Metric-Spaces&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Sets&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Statements&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Terminology&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Topological-Spaces&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Topological-Spaces/Induced&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Topological-Spaces/Terminologies&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Definitions/Vector-Spaces&quot;,&quot;collapsed&quot;:true},{&quot;path&quot;:&quot;Lectures&quot;,&quot;collapsed&quot;:true}]" data-mobile="false" aria-controls="explorer-content" aria-expanded="true"><h2>Explorer</h2><svg xmlns="http://www.w3.org/2000/svg" width="14" height="14" viewBox="5 8 14 8" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="fold"><polyline points="6 9 12 15 18 9"></polyline></svg></button><div id="explorer-content"><ul class="overflow" id="explorer-ul"><li><div class="folder-outer open"><ul style="padding-left:0;" class="content" data-folderul><li><div class="folder-outer "><ul style="padding-left:0;" class="content" data-folderul></ul></div></li><li><div class="folder-container"><svg xmlns="http://www.w3.org/2000/svg" width="12" height="12" viewBox="5 8 14 8" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="folder-icon"><polyline points="6 9 12 15 18 9"></polyline></svg><div data-folderpath="Definitions"><button class="folder-button"><span class="folder-title">Definitions</span></button></div></div><div class="folder-outer "><ul style="padding-left:1.4rem;" class="content" data-folderul="Definitions"><li><div class="folder-container"><svg xmlns="http://www.w3.org/2000/svg" width="12" height="12" viewBox="5 8 14 8" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="folder-icon"><polyline points="6 9 12 15 18 9"></polyline></svg><div data-folderpath="Definitions/Functions"><button class="folder-button"><span class="folder-title">Functions</span></button></div></div><div class="folder-outer "><ul style="padding-left:1.4rem;" class="content" data-folderul="Definitions/Functions"><li><a href="../../Definitions/Functions/Characteristic-Function" data-for="Definitions/Functions/Characteristic-Function">Characteristic Function</a></li><li><a href="../../Definitions/Functions/Direct-Product" data-for="Definitions/Functions/Direct-Product">Direct Product</a></li><li><a href="../../Definitions/Functions/Inverse-Function" data-for="Definitions/Functions/Inverse-Function">Inverse Function</a></li><li><a href="../../Definitions/Functions/Metric" data-for="Definitions/Functions/Metric">Metric</a></li><li><a href="../../Definitions/Functions/Power-Set" data-for="Definitions/Functions/Power-Set">Power Set</a></li></ul></div></li><li><div class="folder-container"><svg xmlns="http://www.w3.org/2000/svg" width="12" height="12" viewBox="5 8 14 8" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="folder-icon"><polyline points="6 9 12 15 18 9"></polyline></svg><div data-folderpath="Definitions/Measure-Theory"><button class="folder-button"><span class="folder-title">Measure Theory</span></button></div></div><div class="folder-outer "><ul style="padding-left:1.4rem;" class="content" data-folderul="Definitions/Measure-Theory"><li><div class="folder-container"><svg xmlns="http://www.w3.org/2000/svg" width="12" height="12" viewBox="5 8 14 8" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="folder-icon"><polyline points="6 9 12 15 18 9"></polyline></svg><div data-folderpath="Definitions/Measure-Theory/Sigma-Algebra"><button class="folder-button"><span class="folder-title">Sigma-Algebra</span></button></div></div><div class="folder-outer "><ul style="padding-left:1.4rem;" class="content" data-folderul="Definitions/Measure-Theory/Sigma-Algebra"><li><a href="../../Definitions/Measure-Theory/Sigma-Algebra/Borel-Measurable" data-for="Definitions/Measure-Theory/Sigma-Algebra/Borel-Measurable">Borel Measurable</a></li><li><a href="../../Definitions/Measure-Theory/Sigma-Algebra/Borel-Sets" data-for="Definitions/Measure-Theory/Sigma-Algebra/Borel-Sets">Borel Sets</a></li><li><a href="../../Definitions/Measure-Theory/Sigma-Algebra/Measurable" data-for="Definitions/Measure-Theory/Sigma-Algebra/Measurable">Measurable</a></li><li><a href="../../Definitions/Measure-Theory/Sigma-Algebra/Measure" data-for="Definitions/Measure-Theory/Sigma-Algebra/Measure">Measure</a></li><li><a href="../../Definitions/Measure-Theory/Sigma-Algebra/Sigma-Algebra" data-for="Definitions/Measure-Theory/Sigma-Algebra/Sigma-Algebra">Sigma-Algebra</a></li></ul></div></li></ul></div></li><li><div class="folder-container"><svg xmlns="http://www.w3.org/2000/svg" width="12" height="12" viewBox="5 8 14 8" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="folder-icon"><polyline points="6 9 12 15 18 9"></polyline></svg><div data-folderpath="Definitions/Metric-Spaces"><button class="folder-button"><span class="folder-title">Metric Spaces</span></button></div></div><div class="folder-outer "><ul style="padding-left:1.4rem;" class="content" data-folderul="Definitions/Metric-Spaces"><li><a href="../../Definitions/Metric-Spaces/Ball" data-for="Definitions/Metric-Spaces/Ball">Ball</a></li><li><a href="../../Definitions/Metric-Spaces/Interior-Point" data-for="Definitions/Metric-Spaces/Interior-Point">Interior Point</a></li><li><a href="../../Definitions/Metric-Spaces/Metric-Space" data-for="Definitions/Metric-Spaces/Metric-Space">Metric Space</a></li></ul></div></li><li><div class="folder-container"><svg xmlns="http://www.w3.org/2000/svg" width="12" height="12" viewBox="5 8 14 8" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="folder-icon"><polyline points="6 9 12 15 18 9"></polyline></svg><div data-folderpath="Definitions/Sets"><button class="folder-button"><span class="folder-title">Sets</span></button></div></div><div class="folder-outer "><ul style="padding-left:1.4rem;" class="content" data-folderul="Definitions/Sets"><li><a href="../../Definitions/Sets/Complex-Numbers" data-for="Definitions/Sets/Complex-Numbers">Complex Numbers</a></li><li><a href="../../Definitions/Sets/Open-Cover" data-for="Definitions/Sets/Open-Cover">Open Cover</a></li><li><a href="../../Definitions/Sets/Open-Map" data-for="Definitions/Sets/Open-Map">Open Map</a></li><li><a href="../../Definitions/Sets/Open-Sets" data-for="Definitions/Sets/Open-Sets">Open Sets</a></li></ul></div></li><li><div class="folder-container"><svg xmlns="http://www.w3.org/2000/svg" width="12" height="12" viewBox="5 8 14 8" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="folder-icon"><polyline points="6 9 12 15 18 9"></polyline></svg><div data-folderpath="Definitions/Statements"><button class="folder-button"><span class="folder-title">Statements</span></button></div></div><div class="folder-outer "><ul style="padding-left:1.4rem;" class="content" data-folderul="Definitions/Statements"><li><a href="../../Definitions/Statements/And" data-for="Definitions/Statements/And">And</a></li><li><a href="../../Definitions/Statements/Implies" data-for="Definitions/Statements/Implies">Implies</a></li><li><a href="../../Definitions/Statements/Not" data-for="Definitions/Statements/Not">Not</a></li><li><a href="../../Definitions/Statements/Or" data-for="Definitions/Statements/Or">Or</a></li></ul></div></li><li><div class="folder-container"><svg xmlns="http://www.w3.org/2000/svg" width="12" height="12" viewBox="5 8 14 8" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="folder-icon"><polyline points="6 9 12 15 18 9"></polyline></svg><div data-folderpath="Definitions/Terminology"><button class="folder-button"><span class="folder-title">Terminology</span></button></div></div><div class="folder-outer "><ul style="padding-left:1.4rem;" class="content" data-folderul="Definitions/Terminology"><li><a href="../../Definitions/Terminology/Algebraically-Complete" data-for="Definitions/Terminology/Algebraically-Complete">Algebraically Complete</a></li><li><a href="../../Definitions/Terminology/Bijective" data-for="Definitions/Terminology/Bijective">Bijective</a></li><li><a href="../../Definitions/Terminology/Bounded" data-for="Definitions/Terminology/Bounded">Bounded</a></li><li><a href="../../Definitions/Terminology/Countable" data-for="Definitions/Terminology/Countable">Countable</a></li><li><a href="../../Definitions/Terminology/Injective" data-for="Definitions/Terminology/Injective">Injective</a></li><li><a href="../../Definitions/Terminology/QED" data-for="Definitions/Terminology/QED">QED</a></li><li><a href="../../Definitions/Terminology/Surjective" data-for="Definitions/Terminology/Surjective">Surjective</a></li></ul></div></li><li><div class="folder-container"><svg xmlns="http://www.w3.org/2000/svg" width="12" height="12" viewBox="5 8 14 8" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="folder-icon"><polyline points="6 9 12 15 18 9"></polyline></svg><div data-folderpath="Definitions/Topological-Spaces"><button class="folder-button"><span class="folder-title">Topological Spaces</span></button></div></div><div class="folder-outer "><ul style="padding-left:1.4rem;" class="content" data-folderul="Definitions/Topological-Spaces"><li><div class="folder-container"><svg xmlns="http://www.w3.org/2000/svg" width="12" height="12" viewBox="5 8 14 8" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="folder-icon"><polyline points="6 9 12 15 18 9"></polyline></svg><div data-folderpath="Definitions/Topological-Spaces/Induced"><button class="folder-button"><span class="folder-title">Induced</span></button></div></div><div class="folder-outer "><ul style="padding-left:1.4rem;" class="content" data-folderul="Definitions/Topological-Spaces/Induced"><li><a href="../../Definitions/Topological-Spaces/Induced/Initial-Topology" data-for="Definitions/Topological-Spaces/Induced/Initial-Topology">Initial Topology</a></li><li><a href="../../Definitions/Topological-Spaces/Induced/Product-Topology" data-for="Definitions/Topological-Spaces/Induced/Product-Topology">Product Topology</a></li><li><a href="../../Definitions/Topological-Spaces/Induced/Separating-Points" data-for="Definitions/Topological-Spaces/Induced/Separating-Points">Separating Points</a></li><li><a href="../../Definitions/Topological-Spaces/Induced/Weakest-Topology" data-for="Definitions/Topological-Spaces/Induced/Weakest-Topology">Weakest Topology</a></li></ul></div></li><li><div class="folder-container"><svg xmlns="http://www.w3.org/2000/svg" width="12" height="12" viewBox="5 8 14 8" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="folder-icon"><polyline points="6 9 12 15 18 9"></polyline></svg><div data-folderpath="Definitions/Topological-Spaces/Terminologies"><button class="folder-button"><span class="folder-title">Terminologies</span></button></div></div><div class="folder-outer "><ul style="padding-left:1.4rem;" class="content" data-folderul="Definitions/Topological-Spaces/Terminologies"><li><a href="../../Definitions/Topological-Spaces/Terminologies/Compact" data-for="Definitions/Topological-Spaces/Terminologies/Compact">Compact</a></li><li><a href="../../Definitions/Topological-Spaces/Terminologies/Connected" data-for="Definitions/Topological-Spaces/Terminologies/Connected">Connected</a></li><li><a href="../../Definitions/Topological-Spaces/Terminologies/Connected-Component" data-for="Definitions/Topological-Spaces/Terminologies/Connected-Component">Connected Component</a></li></ul></div></li><li><a href="../../Definitions/Topological-Spaces/Continuous" data-for="Definitions/Topological-Spaces/Continuous">Continuous</a></li><li><a href="../../Definitions/Topological-Spaces/Hausdorff" data-for="Definitions/Topological-Spaces/Hausdorff">Hausdorff</a></li><li><a href="../../Definitions/Topological-Spaces/Topological-Space" data-for="Definitions/Topological-Spaces/Topological-Space">Topological Space</a></li><li><a href="../../Definitions/Topological-Spaces/Topology" data-for="Definitions/Topological-Spaces/Topology">Topology</a></li><li><a href="../../Definitions/Topological-Spaces/Tychonoff-Theorem" data-for="Definitions/Topological-Spaces/Tychonoff-Theorem">Tychonoff Theorem</a></li></ul></div></li><li><div class="folder-container"><svg xmlns="http://www.w3.org/2000/svg" width="12" height="12" viewBox="5 8 14 8" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="folder-icon"><polyline points="6 9 12 15 18 9"></polyline></svg><div data-folderpath="Definitions/Vector-Spaces"><button class="folder-button"><span class="folder-title">Vector Spaces</span></button></div></div><div class="folder-outer "><ul style="padding-left:1.4rem;" class="content" data-folderul="Definitions/Vector-Spaces"><li><a href="../../Definitions/Vector-Spaces/Complex-Vector-Space" data-for="Definitions/Vector-Spaces/Complex-Vector-Space">Complex Vector Space</a></li><li><a href="../../Definitions/Vector-Spaces/Linear-Basis" data-for="Definitions/Vector-Spaces/Linear-Basis">Linear Basis</a></li><li><a href="../../Definitions/Vector-Spaces/Normed-Vector-Space" data-for="Definitions/Vector-Spaces/Normed-Vector-Space">Normed Vector Space</a></li><li><a href="../../Definitions/Vector-Spaces/Properties-of-a-Vector-Space" data-for="Definitions/Vector-Spaces/Properties-of-a-Vector-Space">Properties of a Vector Space</a></li></ul></div></li><li><a href="../../Definitions/Cauchy-Sequence" data-for="Definitions/Cauchy-Sequence">Cauchy Sequence</a></li><li><a href="../../Definitions/Cauchy-Schwarz-Inequality" data-for="Definitions/Cauchy-Schwarz-Inequality">Cauchy-Schwarz Inequality</a></li><li><a href="../../Definitions/Hilbert-Spaces" data-for="Definitions/Hilbert-Spaces">Hilbert Spaces</a></li><li><a href="../../Definitions/Inner-Product" data-for="Definitions/Inner-Product">Inner Product</a></li><li><a href="../../Definitions/Least-Upper-Bound-Property" data-for="Definitions/Least-Upper-Bound-Property">Least Upper Bound Property</a></li><li><a href="../../Definitions/Linear-Map" data-for="Definitions/Linear-Map">Linear Map</a></li><li><a href="../../Definitions/Nets" data-for="Definitions/Nets">Nets</a></li><li><a href="../../Definitions/Norm" data-for="Definitions/Norm">Norm</a></li><li><a href="../../Definitions/Number-Field" data-for="Definitions/Number-Field">Number Field</a></li><li><a href="../../Definitions/Period-of-a-Fraction" data-for="Definitions/Period-of-a-Fraction">Period of a Fraction</a></li><li><a href="../../Definitions/Rational-Cauchy-Sequences" data-for="Definitions/Rational-Cauchy-Sequences">Rational Cauchy Sequences</a></li><li><a href="../../Definitions/Subcover" data-for="Definitions/Subcover">Subcover</a></li><li><a href="../../Definitions/Subnet" data-for="Definitions/Subnet">Subnet</a></li></ul></div></li><li><div class="folder-container"><svg xmlns="http://www.w3.org/2000/svg" width="12" height="12" viewBox="5 8 14 8" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="folder-icon"><polyline points="6 9 12 15 18 9"></polyline></svg><div data-folderpath="Lectures"><button class="folder-button"><span class="folder-title">Lectures</span></button></div></div><div class="folder-outer "><ul style="padding-left:1.4rem;" class="content" data-folderul="Lectures"><li><a href="../../Lectures/Lecture-1---1.1-Sets-and-Numbers" data-for="Lectures/Lecture-1---1.1-Sets-and-Numbers">Lecture 1 - 1.1 Sets and Numbers</a></li><li><a href="../../Lectures/Lecture-2" data-for="Lectures/Lecture-2">Lecture 2</a></li><li><a href="../../Lectures/Lecture-3" data-for="Lectures/Lecture-3">Lecture 3</a></li><li><a href="../../Lectures/Lecture-4---1.2-Metric-Spaces" data-for="Lectures/Lecture-4---1.2-Metric-Spaces">Lecture 4 - 1.2 Metric Spaces</a></li><li><a href="../../Lectures/Lecture-5" data-for="Lectures/Lecture-5">Lecture 5</a></li><li><a href="../../Lectures/Lecture-6---2.1-Topology" data-for="Lectures/Lecture-6---2.1-Topology">Lecture 6 - 2.1 Topology</a></li><li><a href="../../Lectures/Lecture-7" data-for="Lectures/Lecture-7">Lecture 7</a></li><li><a href="../../Lectures/Lecture-8" data-for="Lectures/Lecture-8">Lecture 8</a></li><li><a href="../../Lectures/Lecture-11" data-for="Lectures/Lecture-11">Lecture 11</a></li><li><a href="../../Lectures/Lecture-12---Induced-Topologies" data-for="Lectures/Lecture-12---Induced-Topologies">Lecture 12 - Induced Topologies</a></li><li><a href="../../Lectures/Lecture-13---Measure-Theory" data-for="Lectures/Lecture-13---Measure-Theory">Lecture 13 - Measure Theory</a></li></ul></div></li></ul></div></li><li id="explorer-end"></li></ul></div></div></div><div class="center"><div class="page-header"><div class="popover-hint"><nav class="breadcrumb-container" aria-label="breadcrumbs"><div class="breadcrumb-element"><a href="../../">Home</a><p> </p></div><div class="breadcrumb-element"><a href="../../Definitions/">Definitions</a><p> </p></div><div class="breadcrumb-element"><a href="../../Definitions/Topological-Spaces/">Topological Spaces</a><p> </p></div><div class="breadcrumb-element"><a href>Topology</a></div></nav><h1 class="article-title">Topology</h1><p show-comma="true" class="content-meta"><time datetime="2025-03-01T15:59:38.420Z">01 Mar 2025</time><span>1 min read</span></p></div></div><article class="popover-hint"><h1 id="definition">Definition<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#definition" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h1>
<p>A collection of subsets of <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6833em;"></span><span class="mord mathnormal" style="margin-right:0.07847em;">X</span></span></span></span>, called <a href="../../Definitions/Sets/Open-Sets" class="internal alias" data-slug="Definitions/Sets/Open-Sets">open sets</a>, such that:</p>
<ol>
<li><span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.9444em;vertical-align:-0.1944em;"></span><span class="mord mathnormal" style="margin-right:0.07847em;">X</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord"></span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel"></span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.4306em;"></span><span class="mord mathnormal" style="margin-right:0.1132em;">τ</span></span></span></span></li>
<li>Any union of sets from <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.4306em;"></span><span class="mord mathnormal" style="margin-right:0.1132em;">τ</span></span></span></span> will be in <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.4306em;"></span><span class="mord mathnormal" style="margin-right:0.1132em;">τ</span></span></span></span>.</li>
</ol>
<blockquote class="callout info is-collapsible is-collapsed" data-callout="info" data-callout-fold>
<div class="callout-title">
<div class="callout-icon"></div>
<div class="callout-title-inner"><p>Info</p></div>
<div class="fold-callout-icon"></div>
</div>
<div class="callout-content">
<p><span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.7335em;vertical-align:-0.1944em;"></span><span class="mord mathnormal" style="margin-right:0.03588em;">y</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal" style="margin-right:0.04398em;">z</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel"></span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.549em;vertical-align:-0.024em;"></span><span class="mord mathnormal" style="margin-right:0.1132em;">τ</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel"></span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.75em;vertical-align:-0.1944em;"></span><span class="mord mathnormal" style="margin-right:0.03588em;">y</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin"></span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:0.5782em;vertical-align:-0.0391em;"></span><span class="mord mathnormal" style="margin-right:0.04398em;">z</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel"></span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.4306em;"></span><span class="mord mathnormal" style="margin-right:0.1132em;">τ</span></span></span></span><br/>
<span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6891em;vertical-align:-0.15em;"></span><span class="mord"><span class="mord mathnormal">x</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3117em;"><span style="top:-2.55em;margin-left:0em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight">i</span></span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel"></span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.549em;vertical-align:-0.024em;"></span><span class="mord mathnormal" style="margin-right:0.1132em;">τ</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel"></span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.8607em;vertical-align:-0.1774em;"></span><span class="mord"><span class="mbin"></span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:0em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight">i</span><span class="mrel mtight"></span><span class="mord mathnormal mtight" style="margin-right:0.07847em;">I</span></span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.1774em;"><span></span></span></span></span></span></span><span class="mord"><span class="mord mathnormal" style="margin-right:0.07847em;">X</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3117em;"><span style="top:-2.55em;margin-left:-0.0785em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight">i</span></span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel"></span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.4306em;"></span><span class="mord mathnormal" style="margin-right:0.1132em;">τ</span></span></span></span></p>
</div>
</blockquote>
<ol start="3">
<li>Any <strong>finite</strong> intersection of sets from <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.4306em;"></span><span class="mord mathnormal" style="margin-right:0.1132em;">τ</span></span></span></span> will be in <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.4306em;"></span><span class="mord mathnormal" style="margin-right:0.1132em;">τ</span></span></span></span>.</li>
</ol>
<blockquote class="callout info is-collapsible is-collapsed" data-callout="info" data-callout-fold>
<div class="callout-title">
<div class="callout-icon"></div>
<div class="callout-title-inner"><p>Info</p></div>
<div class="fold-callout-icon"></div>
</div>
<div class="callout-content">
<p><span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.75em;vertical-align:-0.1944em;"></span><span class="mord mathnormal" style="margin-right:0.03588em;">y</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin"></span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:0.5782em;vertical-align:-0.0391em;"></span><span class="mord mathnormal" style="margin-right:0.04398em;">z</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel"></span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.4306em;"></span><span class="mord mathnormal" style="margin-right:0.1132em;">τ</span></span></span></span><br/>
<span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord"><span class="mbin"></span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:0em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight">i</span><span class="mrel mtight"></span><span class="mord mathnormal mtight" style="margin-right:0.07847em;">I</span></span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.1774em;"><span></span></span></span></span></span></span><span class="mord"><span class="mord mathnormal" style="margin-right:0.07847em;">X</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3117em;"><span style="top:-2.55em;margin-left:-0.0785em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight">i</span></span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel"><span class="mord"><span class="mrel"></span></span><span class="mord vbox"><span class="thinbox"><span class="llap"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="inner"><span class="mord"><span class="mord">/</span><span class="mspace" style="margin-right:0.0556em;"></span></span></span><span class="fix"></span></span></span></span></span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.4306em;"></span><span class="mord mathnormal" style="margin-right:0.1132em;">τ</span></span></span></span></p>
</div>
</blockquote>
<h1 id="examples">Examples<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#examples" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h1>
<blockquote class="callout example" data-callout="example">
<div class="callout-title">
<div class="callout-icon"></div>
<div class="callout-title-inner"><p>Example</p></div>
</div>
<div class="callout-content">
<p>The <strong>topology induced by a metric</strong> on <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6833em;"></span><span class="mord mathnormal" style="margin-right:0.07847em;">X</span></span></span></span> is the collection of all unions of <a href="../../Definitions/Metric-Spaces/Ball" class="internal alias" data-slug="Definitions/Metric-Spaces/Ball">balls</a>.</p>
</div>
</blockquote>
<blockquote class="callout example" data-callout="example">
<div class="callout-title">
<div class="callout-icon"></div>
<div class="callout-title-inner"><p>Reasoning for having point/rule 3 in <a href="#definition" class="internal alias">Definition</a></p></div>
</div>
<div class="callout-content">
<p>Consider the topology on <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6889em;"></span><span class="mord mathbb">R</span></span></span></span> induced by the usual distance.<br/>
<span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord"><span class="mord mathnormal" style="margin-right:0.05017em;">B</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.1514em;"><span style="top:-2.55em;margin-left:-0.0502em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight" style="margin-right:0.02778em;">r</span></span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mopen">(</span><span class="mord mathnormal">x</span><span class="mclose">)</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mopen"></span><span class="mord mathnormal">x</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin"></span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:0.7778em;vertical-align:-0.1944em;"></span><span class="mord mathnormal" style="margin-right:0.02778em;">r</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal">x</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">+</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal" style="margin-right:0.02778em;">r</span><span class="mclose"></span></span></span></span><br/>
Note:<br/>
<span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1.1901em;vertical-align:-0.345em;"></span><span class="mord"><span class="mbin"></span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3322em;"><span style="top:-2.55em;margin-left:0em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight">n</span><span class="mrel mtight"></span><span class="mord mathbb mtight">N</span></span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.1774em;"><span></span></span></span></span></span></span><span class="mopen"></span><span class="mord"></span><span class="mord"><span class="mopen nulldelimiter"></span><span class="mfrac"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.8451em;"><span style="top:-2.655em;"><span class="pstrut" style="height:3em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight">n</span></span></span></span><span style="top:-3.23em;"><span class="pstrut" style="height:3em;"></span><span class="frac-line" style="border-bottom-width:0.04em;"></span></span><span style="top:-3.394em;"><span class="pstrut" style="height:3em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mtight">1</span></span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.345em;"><span></span></span></span></span></span><span class="mclose nulldelimiter"></span></span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord"><span class="mopen nulldelimiter"></span><span class="mfrac"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.8451em;"><span style="top:-2.655em;"><span class="pstrut" style="height:3em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight">n</span></span></span></span><span style="top:-3.23em;"><span class="pstrut" style="height:3em;"></span><span class="frac-line" style="border-bottom-width:0.04em;"></span></span><span style="top:-3.394em;"><span class="pstrut" style="height:3em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mtight">1</span></span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.345em;"><span></span></span></span></span></span><span class="mclose nulldelimiter"></span></span><span class="mclose"></span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mopen">{</span><span class="mord">0</span><span class="mclose">}</span></span></span></span><br/>
(<span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.7329em;vertical-align:-0.1774em;"></span><span class="mord"><span class="mbin"></span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3322em;"><span style="top:-2.55em;margin-left:0em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight">n</span><span class="mrel mtight"></span><span class="mord mathbb mtight">N</span></span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.1774em;"><span></span></span></span></span></span></span></span></span></span> is an infinite intersection of all numbers (in <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6889em;"></span><span class="mord mathbb">N</span></span></span></span>))<br/>
But the reason why this is not <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.3669em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mopen">{</span><span class="mord">0</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal">ε</span><span class="mclose">}</span></span></span></span> is a finite amount of intersections<br/>
<span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal">ε</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel"><span class="mord"><span class="mrel"></span></span><span class="mord vbox"><span class="thinbox"><span class="llap"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="inner"><span class="mord"><span class="mord">/</span><span class="mspace" style="margin-right:0.0556em;"></span></span></span><span class="fix"></span></span></span></span></span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:1.1901em;vertical-align:-0.345em;"></span><span class="mopen"></span><span class="mord"></span><span class="mord"><span class="mopen nulldelimiter"></span><span class="mfrac"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.8451em;"><span style="top:-2.655em;"><span class="pstrut" style="height:3em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight">n</span></span></span></span><span style="top:-3.23em;"><span class="pstrut" style="height:3em;"></span><span class="frac-line" style="border-bottom-width:0.04em;"></span></span><span style="top:-3.394em;"><span class="pstrut" style="height:3em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mtight">1</span></span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.345em;"><span></span></span></span></span></span><span class="mclose nulldelimiter"></span></span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord"><span class="mopen nulldelimiter"></span><span class="mfrac"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.8451em;"><span style="top:-2.655em;"><span class="pstrut" style="height:3em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight">n</span></span></span></span><span style="top:-3.23em;"><span class="pstrut" style="height:3em;"></span><span class="frac-line" style="border-bottom-width:0.04em;"></span></span><span style="top:-3.394em;"><span class="pstrut" style="height:3em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mtight">1</span></span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.345em;"><span></span></span></span></span></span><span class="mclose nulldelimiter"></span></span><span class="mclose"></span></span></span></span> for <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.5782em;vertical-align:-0.0391em;"></span><span class="mord mathnormal">n</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">></span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:1.1901em;vertical-align:-0.345em;"></span><span class="mord"><span class="mopen nulldelimiter"></span><span class="mfrac"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.8451em;"><span style="top:-2.655em;"><span class="pstrut" style="height:3em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight">ε</span></span></span></span><span style="top:-3.23em;"><span class="pstrut" style="height:3em;"></span><span class="frac-line" style="border-bottom-width:0.04em;"></span></span><span style="top:-3.394em;"><span class="pstrut" style="height:3em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mtight">1</span></span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.345em;"><span></span></span></span></span></span><span class="mclose nulldelimiter"></span></span></span></span></span></p>
</div>
</blockquote></article><hr/><div class="page-footer"></div></div><div class="right sidebar"><div class="graph"><h3>Graph View</h3><div class="graph-outer"><div id="graph-container" data-cfg="{&quot;drag&quot;:true,&quot;zoom&quot;:true,&quot;depth&quot;:1,&quot;scale&quot;:1.1,&quot;repelForce&quot;:0.5,&quot;centerForce&quot;:0.3,&quot;linkDistance&quot;:30,&quot;fontSize&quot;:0.6,&quot;opacityScale&quot;:1,&quot;showTags&quot;:true,&quot;removeTags&quot;:[],&quot;focusOnHover&quot;:false,&quot;enableRadial&quot;:false}"></div><button id="global-graph-icon" aria-label="Global Graph"><svg version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px" viewBox="0 0 55 55" fill="currentColor" xml:space="preserve"><path d="M49,0c-3.309,0-6,2.691-6,6c0,1.035,0.263,2.009,0.726,2.86l-9.829,9.829C32.542,17.634,30.846,17,29,17
s-3.542,0.634-4.898,1.688l-7.669-7.669C16.785,10.424,17,9.74,17,9c0-2.206-1.794-4-4-4S9,6.794,9,9s1.794,4,4,4
c0.74,0,1.424-0.215,2.019-0.567l7.669,7.669C21.634,21.458,21,23.154,21,25s0.634,3.542,1.688,4.897L10.024,42.562
C8.958,41.595,7.549,41,6,41c-3.309,0-6,2.691-6,6s2.691,6,6,6s6-2.691,6-6c0-1.035-0.263-2.009-0.726-2.86l12.829-12.829
c1.106,0.86,2.44,1.436,3.898,1.619v10.16c-2.833,0.478-5,2.942-5,5.91c0,3.309,2.691,6,6,6s6-2.691,6-6c0-2.967-2.167-5.431-5-5.91
v-10.16c1.458-0.183,2.792-0.759,3.898-1.619l7.669,7.669C41.215,39.576,41,40.26,41,41c0,2.206,1.794,4,4,4s4-1.794,4-4
s-1.794-4-4-4c-0.74,0-1.424,0.215-2.019,0.567l-7.669-7.669C36.366,28.542,37,26.846,37,25s-0.634-3.542-1.688-4.897l9.665-9.665
C46.042,11.405,47.451,12,49,12c3.309,0,6-2.691,6-6S52.309,0,49,0z M11,9c0-1.103,0.897-2,2-2s2,0.897,2,2s-0.897,2-2,2
S11,10.103,11,9z M6,51c-2.206,0-4-1.794-4-4s1.794-4,4-4s4,1.794,4,4S8.206,51,6,51z M33,49c0,2.206-1.794,4-4,4s-4-1.794-4-4
s1.794-4,4-4S33,46.794,33,49z M29,31c-3.309,0-6-2.691-6-6s2.691-6,6-6s6,2.691,6,6S32.309,31,29,31z M47,41c0,1.103-0.897,2-2,2
s-2-0.897-2-2s0.897-2,2-2S47,39.897,47,41z M49,10c-2.206,0-4-1.794-4-4s1.794-4,4-4s4,1.794,4,4S51.206,10,49,10z"></path></svg></button></div><div id="global-graph-outer"><div id="global-graph-container" data-cfg="{&quot;drag&quot;:true,&quot;zoom&quot;:true,&quot;depth&quot;:-1,&quot;scale&quot;:0.9,&quot;repelForce&quot;:0.5,&quot;centerForce&quot;:0.3,&quot;linkDistance&quot;:30,&quot;fontSize&quot;:0.6,&quot;opacityScale&quot;:1,&quot;showTags&quot;:true,&quot;removeTags&quot;:[],&quot;focusOnHover&quot;:true,&quot;enableRadial&quot;:true}"></div></div></div><div class="toc desktop-only"><button type="button" id="toc" class aria-controls="toc-content" aria-expanded="true"><h3>Table of Contents</h3><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="fold"><polyline points="6 9 12 15 18 9"></polyline></svg></button><div id="toc-content" class><ul class="overflow"><li class="depth-0"><a href="#definition" data-for="definition">Definition</a></li><li class="depth-0"><a href="#examples" data-for="examples">Examples</a></li></ul></div></div><div class="backlinks"><h3>Backlinks</h3><ul class="overflow"><li><a href="../../Definitions/Topological-Spaces/Induced/Weakest-Topology" class="internal">Weakest Topology</a></li><li><a href="../../Lectures/Lecture-11" class="internal">Lecture 11</a></li><li><a href="../../Lectures/Lecture-13---Measure-Theory" class="internal">Lecture 13 - Measure Theory</a></li><li><a href="../../Lectures/Lecture-6---2.1-Topology" class="internal">Lecture 6 - 2.1 Topology</a></li></ul></div></div><footer class><p>Created with <a href="https://quartz.jzhao.xyz/">Quartz v4.4.0</a> © 2025</p><ul><li><a href="https://git.anthonyberg.io/smyalygames/ACIT4330-Page">Gitea</a></li></ul></footer></div></div></body><script type="application/javascript">function c(){let t=this.parentElement;t.classList.toggle("is-collapsed");let l=t.classList.contains("is-collapsed")?this.scrollHeight:t.scrollHeight;t.style.maxHeight=l+"px";let o=t,e=t.parentElement;for(;e;){if(!e.classList.contains("callout"))return;let n=e.classList.contains("is-collapsed")?e.scrollHeight:e.scrollHeight+o.scrollHeight;e.style.maxHeight=n+"px",o=e,e=e.parentElement}}function i(){let t=document.getElementsByClassName("callout is-collapsible");for(let s of t){let l=s.firstElementChild;if(l){l.addEventListener("click",c),window.addCleanup(()=>l.removeEventListener("click",c));let e=s.classList.contains("is-collapsed")?l.scrollHeight:s.scrollHeight;s.style.maxHeight=e+"px"}}}document.addEventListener("nav",i);window.addEventListener("resize",i);
</script><script src="https://cdn.jsdelivr.net/npm/katex@0.16.11/dist/contrib/copy-tex.min.js" type="application/javascript"></script><script type="application/javascript">
const socket = new WebSocket('ws://localhost:3001')
// reload(true) ensures resources like images and scripts are fetched again in firefox
socket.addEventListener('message', () => document.location.reload(true))
</script><script src="../../postscript.js" type="module"></script></html>