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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?

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    $\begingroup$ 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 $x$. $\endgroup$
    – MPW
    May 12, 2021 at 15:44
  • $\begingroup$ @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. $\endgroup$
    – Oliver
    May 12, 2021 at 16:58
  • $\begingroup$ Consider $x\in\mathbb R^{>0}$ $\endgroup$ May 12, 2021 at 20:51

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[Comment converted to answer]

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 $x$).

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