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Can anyone tell me what $\mathbb R^2_{++}$ means? Is it different from $\mathbb R^2_+$?

Thank you so much!

Edit (answer): This is what the author meant (I found it in the lecture notes by the same professor but of a different course): $\mathbb R^2_{++}=\{(x,y)\in\mathbb R^2\mid x>0, y>0\}$ , while $\mathbb R^2_+=\{(x,y)\in\mathbb R^2\mid x≥0, y≥0\}$ .

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    As a follow up: in 2D there is a usual convention for numbering the quadrants. (Though I often forget which is second and which is fourth.) But in higher dimensions I am not aware of any established numbering convention...2012-12-21

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This is not a usual notation, so it should probably be mentioned somewhere, but a reasonable guess would be $\{(x,y)\in\mathbb R^2\mid x>0, y>0\}$.

If you supply more context, and in particular where you have seen this notation perhaps further information can be given.

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    Okay I'll do that. At least now I know this is not a widely accepted notation. Thank you very much.2012-12-21