Definition:Strictly Negative/Real Number

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The strictly negative real numbers are the set defined as:

$\R_{<0} := \set {x \in \R: x < 0}$

That is, all the real numbers that are strictly less than zero.

Also denoted as

The $\mathsf{Pr} \infty \mathsf{fWiki}$-specific notation $\R_{<0}$ is actually non-standard. The conventional symbol to denote this concept is $\R_-^*$.

Note that $\R^-$ is also seen sometimes, but this is usually interpreted as the set $\set {x \in \R: x \le 0}$.

Some sources, particularly those whose treatment is topological, use $\bar \R_+$.

Some sources merely refer to this as negative, as their treatments do not accept $0$ as being either negative or positive.