Let $S = (X, \times)$ be an
D21: Algebraic structure such that
| (i) |
\begin{equation}
X \neq \emptyset
\end{equation}
|
A
D2218: Set element $y \in X$ is a
left identity element in $S$ if and only if
\begin{equation}
\forall \, x \in X : y x = x
\end{equation}
