From 7c66b227a494748e2a546fb85317accd00aebe53 Mon Sep 17 00:00:00 2001 From: Justin Gassner Date: Thu, 15 Feb 2024 05:11:07 +0100 Subject: Update --- pages/general-topology/topological-spaces.md | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) (limited to 'pages/general-topology/topological-spaces.md') diff --git a/pages/general-topology/topological-spaces.md b/pages/general-topology/topological-spaces.md index b0b1834..cb0c30b 100644 --- a/pages/general-topology/topological-spaces.md +++ b/pages/general-topology/topological-spaces.md @@ -75,7 +75,8 @@ is the smallest topology on $X$ containing $\mathcal{A}$. {% definition Basis for a Topology %} A *basis for a topology* on a set $X$ is a collection $\mathcal{B}$ of subsets of $X$ -such that for every point $x \in X$ +such that for every point $x \in X$ + - there exists $B \in \mathcal{B}$ such that $x \in B$, - if $x \in B_1 \cap B_2$ for $B_1, B_2 \in \mathcal{B}$, then there exists a $B_3 \in \mathcal{B}$ @@ -85,6 +86,7 @@ such that for every point $x \in X$ {% theorem Topology Generated by a Basis %} If $X$ is set and $\mathcal{B}$ is a basis for a topology on $X$, then the topology generated by $\mathcal{B}$ equals + - the collection of all subsets $S \subset X$ with the property that for every $x \in S$ there exists a basis element $B \in \mathcal{B}$ such that $x \in B$ and $B \subset S$; @@ -125,7 +127,7 @@ then the topology generated by $\mathcal{S}$ equals Suppose $(X,\mathcal{T})$ is a topological space. A subset $S$ of $X$ is called *open* with respect to $\mathcal{T}$ -when it belongs to $\mathcal{T}$ +when it belongs to $\mathcal{T}$, and it is called *closed* with respect to $\mathcal{T}$ when its complement $X \setminus S$ belongs to $\mathcal{T}$. {% enddefinition %} @@ -137,10 +139,8 @@ if and only if its complement is closed. Let $\mathcal{C}$ be the collection of closed subsets of a topological space. Then {: .mb-0 } - $X$ and $\varnothing$ belong to $\mathcal{C}$, -- the intersection of any subcollection of $\mathcal{C}$ belongs to $\mathcal{C}$, -- the union of any finite subcollection $\mathcal{C}$ belongs to $\mathcal{C}$. +- the intersection of any subcollection of $\mathcal{C}$ belongs to $\mathcal{C}$, +- the union of any finite subcollection $\mathcal{C}$ belongs to $\mathcal{C}$. {% endproposition %} ## The Subspace Topology - - -- cgit v1.2.3-54-g00ecf