# group theory definition

## properties

Before introduce group definition, let me list those properties mentioned.

1. Closure:
For all $a, b \in G$, the relation $a \bullet b \in G$ holds.
2. associative:
For all $a, b, c \in G$, the equation $(a \bullet b) \bullet c = a \bullet (b \bullet c)$ holds.
3. Commutative
For all $a, b \in G$, $a \bullet b = b \bullet a$.
4. Identity element:
There exists an element $e \in G$, such that for all elements $a \in G$, the equation $e \bullet a = a$ holds.
5. Inversible:
For each $a \in G$, there exists an element $a^{-1} \in G$ such that $a \bullet a^{-1} = e$, where $e$ is the identity element.
6. Distributive:
For all $a, b, c \in G$, the equation $(a+b) \bullet c=a \bullet c+b \bullet c$ holds.

## group(G,•)

consists of a set of elements together with an operation $\bullet$ such that:

property $\bullet$
clojure $\checkmark$
associative $\checkmark$
identity $\checkmark$
inversible $\checkmark$
commutative $\times$
distributive $\times$

## abelian group (A, •)

Abelian group is a group, but also have one additional property:

property $\bullet$
clojure $\checkmark$
associative $\checkmark$
identity $\checkmark$
inversible $\checkmark$
commutative $\checkmark$
distributive $\times$

## rings

A commutative ring with unity $(R,+,*)$ is an algebraic structure consisting of a set of elements R together with two binary operations denoted + and * which satisfy the follow properties for all elements in R:

property $+$ $*$
clojure $\checkmark$ $\checkmark$
associative $\checkmark$ $\checkmark$
commutative $\checkmark$ $\checkmark$
identity $\checkmark$ $\checkmark$
inversible $\checkmark$ N/A
distributive $\times$ $\checkmark$

## ideal ring

Let $(R,+,*)$ be a ring; A non-empty subset $I$ of $R$ called a ideal of the ring if:

1. $(I,+)$ is a group.
2. $i*r \in I$ for all $i \in I$ and $r \in R$.
property $+$
clojure $\checkmark$
associative $\checkmark$
identity $\checkmark$
inversible $\checkmark$
commutative $\times$
distributive $\times$

## field

field is a set of elements which is closed under two binary operations, which we denote by $+$ and $\times$.

property $+$ $\times$
clojure $\checkmark$ $\checkmark$
associative $\checkmark$ $\checkmark$
commutative $\checkmark$ $\checkmark$
identity 0 1
inversible $\checkmark$ !0
distributive $\times$ $\checkmark$

group theory definition
https://rugal.github.com/2014/2014-11-04-group-theory-definition/
Author
Rugal Bernstein
Posted on
November 4, 2014