# What does $\mathbb{R}_{++}$ stand for?

What does $\mathbb{R}_{++}$ mean?

I know $\mathbb{R}_+$ means all non-negative real numbers, but I have no clue what $\mathbb{R}_{++}$ means.

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I don't think it is standard notation. Where have you seen it? –  Henning Makholm Sep 2 '12 at 20:24
I would say: Look in the previous pages of that book. –  GEdgar Sep 2 '12 at 21:01
Maybe it's a programming language... :-) –  Asaf Karagila Sep 2 '12 at 21:46

It usually means the set of all positive real numbers, $\mathbb{R}_{++} = (0,\infty)$. Of course, there might be more symbols for this set.

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Right, because $\mathbb{R}_{+}$ is ambiguous, as some authors use it for $[0,\infty)$ and some for $(0,\infty)$. –  cyberSingularity Sep 2 '12 at 21:43
I have seen it used this way fairly often. –  Michael Greinecker Sep 2 '12 at 21:45
--in economics books. –  Michael Greinecker Sep 2 '12 at 21:54