Started reading Diffusions, Markov Processes, and Martingales: Volume 1, Foundations (Cambridge Mathematical Library) and at the beginning of the section titled "Some Frequently Used Notation" I see there is a set defined to be equal to the interval from 0 to infinity, exclusive, shown as the real numbers symbol with a double plus superscript:
From context, $\Bbb{R}^+$ is non-negative real numbers, and $\Bbb{R}^{++}$ is positive real numbers. However, I'd never seen this notation before and was wondering
(a) Is this standard notation?
(b) Is the above is how it is actually to be interpreted?
Thank you!