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authorBen Levy <7348004+io12@users.noreply.github.com>2020-07-04 22:46:46 -0400
committerGitHub <noreply@github.com>2020-07-04 22:46:46 -0400
commit081cf637cc730b04a3c24fa7c630e5b030b614c4 (patch)
treee6b7cddc4ad41ff0940621c98104ab7a0cb931e9 /set-theory.html.markdown
parentef0480286342219c7a592926660018534f5af12a (diff)
Fix set theory formatting issues
Diffstat (limited to 'set-theory.html.markdown')
-rw-r--r--set-theory.html.markdown19
1 files changed, 19 insertions, 0 deletions
diff --git a/set-theory.html.markdown b/set-theory.html.markdown
index 988c4397..c6bc39c5 100644
--- a/set-theory.html.markdown
+++ b/set-theory.html.markdown
@@ -29,11 +29,13 @@ These operators don't require a lot of text to describe.
* `Z`, the set of all integers. `{…,-2,-1,0,1,2,…}`
* `Q`, the set of all rational numbers.
* `R`, the set of all real numbers.
+
### The empty set
* The set containing no items is called the empty set. Representation: `∅`
* The empty set can be described as `∅ = {x|x ≠ x}`
* The empty set is always unique.
* The empty set is the subset of all sets.
+
```
A = {x|x∈N,x < 0}
A = ∅
@@ -42,6 +44,7 @@ A = ∅
|∅| = 0
|{∅}| = 1
```
+
## Representing sets
### Enumeration
* List all items of the set, e.g. `A = {a,b,c,d}`
@@ -49,6 +52,7 @@ A = ∅
### Description
* Describes the features of all items in the set. Syntax: `{body|condtion}`
+
```
A = {x|x is a vowel}
B = {x|x ∈ N, x < 10l}
@@ -84,6 +88,7 @@ C = {2x|x ∈ N}
* The number of items in a set is called the base number of that set. Representation: `|A|`
* If the base number of the set is finite, this set is a finite set.
* If the base number of the set is infinite, this set is an infinite set.
+
```
A = {A,B,C}
|A| = 3
@@ -94,6 +99,7 @@ B = {a,{b,c}}
### Powerset
* Let `A` be any set. The set that contains all possible subsets of `A` is called a powerset (written as `P(A)`).
+
```
P(A) = {x|x ⊆ A}
@@ -103,41 +109,54 @@ P(A) = {x|x ⊆ A}
## Set operations among two sets
### Union
Given two sets `A` and `B`, the union of the two sets are the items that appear in either `A` or `B`, written as `A ∪ B`.
+
```
A ∪ B = {x|x∈A∨x∈B}
```
+
### Intersection
Given two sets `A` and `B`, the intersection of the two sets are the items that appear in both `A` and `B`, written as `A ∩ B`.
+
```
A ∩ B = {x|x∈A,x∈B}
```
+
### Difference
Given two sets `A` and `B`, the set difference of `A` with `B` is every item in `A` that does not belong to `B`.
+
```
A \ B = {x|x∈A,x∉B}
```
+
### Symmetrical difference
Given two sets `A` and `B`, the symmetrical difference is all items among `A` and `B` that doesn't appear in their intersections.
+
```
A △ B = {x|(x∈A∧x∉B)∨(x∈B∧x∉A)}
A △ B = (A \ B) ∪ (B \ A)
```
+
### Cartesian product
Given two sets `A` and `B`, the cartesian product between `A` and `B` consists of a set containing all combinations of items of `A` and `B`.
+
```
A × B = { {x, y} | x ∈ A, y ∈ B }
```
+
## "Generalized" operations
### General union
Better known as "flattening" of a set of sets.
+
```
∪A = {x|X∈A,x∈X}
∪A={a,b,c,d,e,f}
∪B={a}
∪C=a∪{c,d}
```
+
### General intersection
+
```
∩ A = A1 ∩ A2 ∩ … ∩ An
```