# Notation indicating a number is negative, positive, or zero.

We can indicate that $$x$$ is negative by writing $$x<0$$, that it is positive by writing $$x>0$$, or that it is zero by writing $$x=0$$.

Out of curiosity, are there other notations, such as an overset or underset, to say the same?

• Those conditions are precisely the definitions of a number being negative, positive, or zero. You can always use or create equivalent statements, such as $x\in\mathbb R^+$ or $\operatorname{sgn}(x) = 1$ (the latter referring to the signum function which takes values $-1$, $1$, or $0$ corresponding to $x$ being negative, positive, or zero -- essentially, the "sign" of $x$.
– MPW
May 12, 2021 at 15:44
• @MPW Sounds like a great answer. If you post it as one, I will mark it. I definitely see how $x\in\mathbb{R}^+$ makes sense. May 12, 2021 at 16:58
• Consider $x\in\mathbb R^{>0}$ May 12, 2021 at 20:51

You can always use or create equivalent statements, such as $$x\in\mathbb R^+$$ or $$\operatorname{sgn}(x) = 1$$ (the latter referring to the signum function which takes values $$-1$$, $$1$$, or $$0$$ corresponding to $$x$$ being negative, positive, or zero -- essentially, the "sign" of $$x$$).