User:Dfeuer/Cone Condition Equivalent to Congruence
This page has been identified as a candidate for refactoring. Until this has been finished, please leave {{Refactor}} in the code.
New contributors: Refactoring is a task which is expected to be undertaken by experienced editors only. Because of the underlying complexity of the work needed, it is recommended that you do not embark on a refactoring task until you have become familiar with the structural nature of pages of $\mathsf{Pr} \infty \mathsf{fWiki}$.To discuss this page in more detail, feel free to use the talk page. When this work has been completed, you may remove this instance of {{Refactor}} from the code. |
Theorem
Let $(G,\circ)$ be a group with identity $e$.
Let $C$ be a cone compatible with $\circ$ with the following properties:
- $C = C^{-1}$
- $e \in C$
Let $\cong$ be the relation induced by $C$.
Then $\cong$ is a Congruence Relation.
Proof
By User:Dfeuer/Cone Compatible with Group Induces Transitive Compatible Relation, $\cong$ is compatible with $\circ$ and is transitive.
By User:Dfeuer/Cone Condition Equivalent to Symmetry and User:Dfeuer/Cone Condition Equivalent to Reflexivity, $\cong$ is symmetric and reflexive.
Thus $\cong$ is an Equivalence Relation compatible with $\circ$, and hence a congruence relation.
$\blacksquare$
Theorem
Let $(G,\circ)$ be a group with identity $e$.
Let $\cong$ be a Congruence Relation on $G$.
Then there is a unique cone $C$ compatible with $\circ$ such that $C$ induces $\cong$, and $C$ has the following properties:
- $C = C^{-1}$
- $e \in C$
Proof
Since a congruence relation on $G$ is an equivalence relation compatible with $\circ$, it is in particular transitive.
Thus by User:Dfeuer/Transitive Relation Compatible with Group Operation Induced by Unique Cone $\cong$ is induced by a unique cone
- $C = \{x \in G: e \cong x\}$
That is, $C$ is the $\cong$ congruence class of $e$.
By User:Dfeuer/Cone Condition Equivalent to Symmetry:
- $C = C^{-1}$
Finally, by User:Dfeuer/Cone Condition Equivalent to Reflexivity:
- $e \in C$
$\blacksquare$