# What does $R_{0}^{+}$ mean?

I'm reading this paper: http://www.aaai.org/Papers/KDD/1996/KDD96-027.pdf, and the authors used the symbol $R_{0}^{+}$ in the definition of Exact Exception Problem, such as $D: P(I) \rightarrow R_{0}^{+}$. Could anyone please help me understand what the symbol $R_{0}^{+}$ means? It seems refer to the set of real numbers, but if that's the case, what are the subscript and superscript for?

Thanks,

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I am not fully sure but I carefully understand the paper it seems to me that $R_{0}^{+}$ denotes set of all positive real number except $0$ means $(0,\infty)$.(I conclude it from cardinality functio) – iostream007 Jul 20 '13 at 20:53

It is the half line $[0,+\infty)$.
$\mathbb R^+$ alone denotes the positive real numbers, and the subscript we see here $0$ denotes the inclusion of zero, as well. So all together, we have the set $$\mathbb R_0^+ = \{x\mid x\in \mathbb R, x\geq 0\}$$
This set is sometimes denoted by $\mathbb R_{\geq 0}$. There is no one universally used notation to describe the set of non-negative real numbers. So it's usually best that authors define the notation they plan to use.