From 16555851b6514a736c5c9d8e73de7da7fc9b6288 Mon Sep 17 00:00:00 2001 From: Prefetch Date: Thu, 20 Oct 2022 18:25:31 +0200 Subject: Migrate from 'jekyll-katex' to 'kramdown-math-sskatex' --- source/know/concept/sigma-algebra/index.md | 44 +++++++++++++++--------------- 1 file changed, 22 insertions(+), 22 deletions(-) (limited to 'source/know/concept/sigma-algebra') diff --git a/source/know/concept/sigma-algebra/index.md b/source/know/concept/sigma-algebra/index.md index 5ba7b14..ac607a7 100644 --- a/source/know/concept/sigma-algebra/index.md +++ b/source/know/concept/sigma-algebra/index.md @@ -8,15 +8,15 @@ categories: layout: "concept" --- -In set theory, given a set $\Omega$, a $\sigma$**-algebra** -is a family $\mathcal{F}$ of subsets of $\Omega$ +In set theory, given a set $$\Omega$$, a $$\sigma$$**-algebra** +is a family $$\mathcal{F}$$ of subsets of $$\Omega$$ with these properties: -1. The full set is included $\Omega \in \mathcal{F}$. -2. For all subsets $A$, if $A \in \mathcal{F}$, - then its complement $\Omega \!-\! A \in \mathcal{F}$ too. -3. If two events $A, B \in \mathcal{F}$, - then their union $A \cup B \in \mathcal{F}$ too. +1. The full set is included $$\Omega \in \mathcal{F}$$. +2. For all subsets $$A$$, if $$A \in \mathcal{F}$$, + then its complement $$\Omega \!-\! A \in \mathcal{F}$$ too. +3. If two events $$A, B \in \mathcal{F}$$, + then their union $$A \cup B \in \mathcal{F}$$ too. This forms a Boolean algebra: property (1) represents TRUE, @@ -24,28 +24,28 @@ property (1) represents TRUE, and that is all we need to define all logic. For example, FALSE and OR follow from the above points: -4. The empty set is included $\varnothing \in \mathcal{F}$. -5. If two events $A, B \in \mathcal{F}$, - then their intersection $A \cap B \in \mathcal{F}$ too. +4. The empty set is included $$\varnothing \in \mathcal{F}$$. +5. If two events $$A, B \in \mathcal{F}$$, + then their intersection $$A \cap B \in \mathcal{F}$$ too. -For a given $\Omega$, there are typically multiple valid $\mathcal{F}$, +For a given $$\Omega$$, there are typically multiple valid $$\mathcal{F}$$, in which case you need to specify your choice. -Usually this would be the smallest $\mathcal{F}$ +Usually this would be the smallest $$\mathcal{F}$$ (i.e. smallest family of subsets) that contains all subsets of special interest for the topic at hand. -Likewise, a **sub-$\sigma$-algebra** -is a sub-family of a certain $\mathcal{F}$, -which is a valid $\sigma$-algebra in its own right. - -A notable $\sigma$-algebra is the **Borel algebra** $\mathcal{B}(\Omega)$, -which is defined when $\Omega$ is a metric space, -such as the real numbers $\mathbb{R}$. -Using that as an example, the Borel algebra $\mathcal{B}(\mathbb{R})$ +Likewise, a **sub-$$\sigma$$-algebra** +is a sub-family of a certain $$\mathcal{F}$$, +which is a valid $$\sigma$$-algebra in its own right. + +A notable $$\sigma$$-algebra is the **Borel algebra** $$\mathcal{B}(\Omega)$$, +which is defined when $$\Omega$$ is a metric space, +such as the real numbers $$\mathbb{R}$$. +Using that as an example, the Borel algebra $$\mathcal{B}(\mathbb{R})$$ is defined as the family of all open intervals of the real line, -and all the subsets of $\mathbb{R}$ obtained by countable sequences +and all the subsets of $$\mathbb{R}$$ obtained by countable sequences of unions and intersections of those intervals. -The elements of $\mathcal{B}$ are **Borel sets**. +The elements of $$\mathcal{B}$$ are **Borel sets**. -- cgit v1.2.3