(i) | \begin{equation} X \neq \emptyset \end{equation} |
(1) | \begin{equation} \forall \, x \in X : y + x = x \end{equation} | (D537: Left identity element) |
(2) | \begin{equation} \forall \, x \in X : x + y = x \end{equation} | (D538: Right identity element) |