Zero Complement is Not Empty

Theorem
Let $\struct {S, \circ, \preceq}$ be a naturally ordered semigroup.

Let $S^*$ be the zero complement of $S$.

Then $S^*$ is not empty.

Proof
From axiom $(NO4)$, we have:


 * $\exists m, n \in S: m \ne n$

That is, there are at least two distinct elements in $S$.

Therefore, there must be at least one element in $S^* = S \setminus \set 0$.

So:
 * $S^* = S \setminus \set 0 \ne \O$