User:Jshflynn/Empty Word is Two-sided Identity
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Theorem
Let $\Sigma$ be an alphabet.
Let $x$ be a word over $\Sigma$, $\lambda$ be the empty word over $\Sigma$ and $\circ$ denote concatenation.
Then $\lambda$ is a two-sided identity element of concatenation. That is,
- $x \circ \lambda = x$ and $\lambda \circ x = x$
Proof
Follows immediately from the definition of concatenation with the empty word.
$\blacksquare$