Composition of Regular Representations

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Theorem

Let $\struct {S, *}$ be a semigroup.

Let $\lambda_x, \rho_x$ be the left and right regular representations of $\struct {S, *}$ with respect to $x$.

Let $\lambda_x \circ \lambda_y$, $\rho_x \circ \rho_y$ etc. be defined as the composition of the mappings $\lambda_x$ and $\lambda_y$ etc.


Then $\forall x, y \in S$, the following results hold:

Composition of Left Regular Representations

$\lambda_x \circ \lambda_y = \lambda_{x * y}$

Composition of Right Regular Representations

$\rho_x \circ \rho_y = \rho_{y * x}$

Composition of Left Regular Representation with Right

$\lambda_x \circ \rho_y = \rho_y \circ \lambda_x$