Regular Representation on Subgroup is Bijection to Coset/Left
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Theorem
Let $G$ be a group.
Let $H$ be a subgroup of $G$.
Let $x, y \in G$.
Let $y H$ denote the left coset of $H$ by $y$.
The mapping $\lambda_x: H \to x H$, where $\lambda_x$ is the left regular representation of $H$ with respect to $x$, is a bijection from $H$ to $x H$.
Proof
Let $h \in H$.
Then:
- $\map {\lambda_x} h = x h \in x H$
Thus:
- $\forall h \in H: \map {\lambda_x} h \in x H$
demonstrating that $\lambda_x: H \to x H$ is a mapping.
A permutation is a bijection by definition.
As Regular Representations in Group are Permutations, it follows that $\lambda_x$ is a bijection.
$\blacksquare$
Sources
- 1965: Seth Warner: Modern Algebra ... (previous) ... (next): Chapter $\text {IV}$: Rings and Fields: $25$. Cyclic Groups and Lagrange's Theorem