(i) | $x^+$ is a D589: Successor set of $x$ for any $x \in \mathbb{N}$ |
A D554: Binary operation $\cdot : \mathbb{N} \times \mathbb{N} \to \mathbb{N}$ is a natural number multiplication operation if and only if
(1) | \begin{equation} \forall \, n \in \mathbb{N} : n \cdot 0 = 0 \end{equation} |
(2) | \begin{equation} \forall \, n, m \in \mathbb{N} : n \cdot m^+ = n \cdot m + n \end{equation} |